Smartphone addiction is a new behavioral addiction. Smartphone addiction, also known as “smartphone use disorder” or “problematic use of smartphone,” has the following characteristics: (a) smartphone use is out of control, such as using smartphones too frequently or being unable to control the use of smartphones on important occasions (Park and Lee, 2011; Lin et al., 2014); (b) psychological dependence on smartphones, paying too much attention to smartphones (Montag and Reuter, 2017); and (c) negative effects on individuals’ interpersonal communication, study, work, physical health, and mental health (Lin et al., 2014, 2016). Consequently, given the above characteristics of smartphone addiction, it is crucial to explore the mechanism of smartphone addiction among college students, especially female college students.

Meaning therapy theory of Frankl (1963) suggests that the fundamental drive of human existence is to constantly seek the meaning and purpose of life to satisfy psychological needs, and the meaning in life is the basic element for an individual to experience happiness in life. Meaning in life refers to “the sense made of, and significance felt regarding, the nature of one’s being and existence” (Steger et al., 2006, p. 81). Steger and Frazier (2005) indicated that the stronger an individual’s meaning in life, the lower the possibility of addictive behaviors. People with low levels of meaning in life lack the motivation and goal to pursue the meaning of life, so it is easy for them to fill the gaps in their lives with some addictive behaviors (Thege et al., 2013; Eryilmaz, 2014; Zhang et al., 2015; Yao et al., 2016; Çevik et al., 2020; Zhao et al., 2020; Hu et al., 2022). Recent studies have provided empirical evidence for the relationship between meaning in life and smartphone addiction; that is, meaning in life was negatively related to college students’ smartphone addiction (Çevik et al., 2020; Hu et al., 2022).

School adjustment is a very important development task in the process of students’ growth, which is closely related to the meaning in life and smartphone addiction. School adjustment is defined as the process of happily participating in various school activities and achieving academic achievements in the school context (Ladd et al., 1997). As for the structural components of school adjustment, most scholars agree that school adjustment should include campus life adjustment, learning adjustment, emotional adjustment, and interpersonal adjustment (Zeng, 2009). Meaning in life theory suggests that a higher level of meaning in life promotes optimal adjustment across domains of functioning, including physical health, well-being, and academic achievement (Roepke et al., 2014; Glaw et al., 2017; Hooker et al., 2018). This notion has been supported by empirical studies among adolescents, young adults, and elderly people (Kleiman et al., 2013; Henry et al., 2014; Czekierda et al., 2017, 2019). Since college students spend most of their time in universities, school adjustment is a very important part of college students’ social adjustment. Previous studies have examined the relationship between meaning in life and a certain factor of school adjustment among college students. For example, one previous study has indicated that undergraduate students whose meaning in life is threatened experienced greater stress than those whose meaning in life is intact (Park and Baumeister, 2016). Meaning in life is also closely related to emotional adjustment. Some scholars have verified that meaning in life has a positive effect on college students’ life satisfaction (Steger et al., 2011; Lin, 2020) and well-being (McMahan and Renken, 2011). Besides, meaning in life is negatively related to college students’ depression and anxiety (Lin, 2020). However, there are few studies on the direct relationship between meaning in life and college students’ school adjustment. Up until now, only Li et al. (2022) conducted a three-wave longitudinal study among freshmen to explore the relationship between meaning in life and school adjustment, and the results showed that meaning in life was positively related to freshmen’s school adjustment. Thus, future research needs to explore the direct relationship between meaning in life and school adjustment on the basis of expanding the sampling range of college students.

Self-determination theory proposes that after an individual’s basic psychological needs are satisfied, his or her social adjustment will be better, and then his or her risk of addiction will be lower (Deci and Ryan, 2000; Duchesne et al., 2016; Ryan and Deci, 2017). If individuals cannot satisfy their psychological needs in social situations, they are prone to maladjustment, and maladjustment is likely to lead them to seek substitutes and compensation in other fields (Deci and Ryan, 2000; Kuzucu and Şimşek, 2013), which easily leads to addictive behaviors (Verstuyf et al., 2013; Li et al., 2016; Settley, 2020). Smartphones have the following functional characteristics: (a) collectivity of functions (Kwon et al., 2013a,b); (b) personalization and customization of content (Kim, 2013; Lin et al., 2014; Mok et al., 2014); (c) accessibility (Wu et al., 2013; Ahn and Jung, 2016); and (d) convenience (Wu et al., 2013; Ahn and Jung, 2016). Since smartphones have the above functional characteristics, it is easy to obtain alternative satisfaction or compensation by using smartphones when individuals are prone to maladjustment. However, excessive use of smartphones easily leads to addiction (Ahn and Jung, 2016). Some empirical studies support the notion of self-determination theory. For example, with regard to the relationship between emotional adjustment and college students’ smartphone addiction, some studies have reported that depression (Aker et al., 2017; Boumosleh and Jaalouk, 2017; Kim et al., 2017), anxiety (Aker et al., 2017; Boumosleh and Jaalouk, 2017; Kim et al., 2017), and loneliness (Kim et al., 2017; Alinejad et al., 2022) are positively related to college students’ smartphone addiction. Moreover, one empirical research confirmed that alexithymia not only directly affected college students’ smartphone addiction, but also indirectly affected their smartphone addiction through depression, anxiety, and stress (Gao et al., 2018). As for the relationship between learning adjustment and smartphone addiction, scholars verified that learning boredom has a positive effect on the smartphone addiction of college students (Bian et al., 2018). Moreover, a recent study has revealed that the higher the perceived academic pressure of college students, the more serious their smartphone addiction is (Zhang et al., 2022). Interpersonal adjustment is also closely associated with college students’ smartphone addiction. Previous studies have consistently verified that interpersonal adjustment is negatively related to smartphone addiction; that is, the better the interpersonal adjustment of college students, the lower their risk of smartphone addiction (Zhang Y. L. et al., 2017; Zhang Y. et al., 2017; Zhang et al., 2018a,b; Li et al., 2021). Summarizing the above studies, these studies mainly explored the relationship between a certain factor of school adjustment and smartphone addiction, but there was a lack of direct research on the relationship between school adjustment and smartphone addiction.

In summary, although previous studies have examined the relationship between college students’ meaning in life and freshmen’s school adjustment or a certain factor of college students’ school adjustment and the relationship between a certain factor of school adjustment and college students’ smartphone addiction, there is a lack of empirical study among female college students to explore: (a) the relationship between meaning in life and school adjustment; (b) the relationship between school adjustment and smartphone addiction; and (c) the mediating role of school adjustment in the relationship between meaning in life and smartphone addiction.

Grade differences in psychology and behavior are a very important field of psychological research. Some studies have examined the grade differences in Chinese college students’ smartphone addiction (Xie and Wang 2015; Jiang and Li, 2020). Specifically, Chinese college students’ smartphone addiction shows a trend of first increasing (from freshman year to sophomore year), then decreasing (from sophomore year to junior year), and then rising (from junior year to senior year), among which sophomores’ smartphone addiction is the most serious, followed by seniors, and freshmen and juniors have the lowest level of smartphone addiction (Xie and Wang 2015; Jiang and Li, 2020). As for the grade differences in meaning in life, some recent studies found that freshmen had the highest level of meaning in life, followed by juniors and seniors, and sophomores had the lowest level of meaning in life (Zhang and Zhou, 2020; Xie, 2021). Grade differences also exist in Chinese college students’ school adjustment. Scholars found that the school adjustment of freshmen and juniors is significantly stronger than that of sophomores (Pang and Wu, 2012). One empirical study compared the differences in college students’ school adjustment among four grades and confirmed that the school adjustment of sophomores is significantly lower than that of the other three grades (Chao, 2008). Besides, one study further revealed that the scores of freshmen and juniors are significantly higher than those of sophomores in interpersonal relationships, career adjustment, emotional adjustment, and self-adjustment (Meng, 2014). To sum up the above studies, grade differences in meaning in life, school adjustment and smartphone addiction among college students are as follows:

College stage is an important period for college students to complete their identity as “college students.” Identity can be conceptualized as a way to understand some parts or aspects of self-concept (Oyserman and Markus, 1998; Hogg, 2003). Identity-based motivation theory proposes that people will behave in a way consistent with the identity initiated in a certain situation. People adopt certain behaviors or do not adopt certain behaviors, which are influenced by the identity perception initiated in a certain situation (Oyserman, 2009a,b). It needs to be emphasized that this kind of identity initiated by a certain situation is not always stable, and the formation of identity is influenced by the degree to which possible selves conforms to the external environment requirements (Bruner, 1990, 1995; Li and Liu, 2010; Crocetti et al., 2012). Possible selves are the individual’s self-relevant expectations for the future, which can predict and inspire people’s actions (Oyserman and Markus, 1990). When possible selves conforms to the external environment requirements, individuals will form a healthy identity, which will help to establish the meaning and purpose of life, and then make individuals show good social adjustment (Marcia, 1966; Erikson, 1968, 1975; Steger et al., 2009). When possible selves conflicts with the external environmental requirements, individuals may have identity crisis, which will lead to the loss of individual’s meaning in life, and then lead to a series of negative consequences such as social maladjustment and lack of sense of belonging and responsibility (Marcia, 1966; Erikson, 1968, 1975; Steger et al., 2009; Li and Liu, 2010). College students have to face different challenges in their 3 or 4 years of college life. Freshmen who have just entered the university need to adapt to university life quickly (Lu, 2015; Zhang Y. L. et al., 2017; Zhang Y. et al., 2017). Sophomores may easily fall into the “sophomore slump” due to various internal and external factors (Gahagan and Stuart Hunter, 2008; Kennedy and Upcraft, 2010; Wang and Kennedy-Phillips, 2013; Webb and Cotton, 2018). Besides, juniors and seniors need to face the pressure of further education and employment (Lu, 2015; Zhang Y. L. et al., 2017; Zhang Y. et al., 2017). Besides being influenced by individual factors, the development of individual’s possible selves is also influenced by the social environment in which they live (Bruner, 1990, 1995; Crocetti et al., 2012). Consequently, facing the above-mentioned “challenges” of different grades, the possible selves of college students in different grades may be different. Combining the meaning therapy theory, the meaning in life theory, the self-determination theory, and the identity-based motivation theory, we can understand that the degree of conformity between college students’ possible selves and the school environment requirements in different grades may lead to different results of their identity (healthy identity or identity crisis), and then make college students in different grades have different levels of meaning in life. Different levels of meaning in life of college students in different grades may have different direct effects on their smartphone addiction. Moreover, in different grades, different levels of meaning in life of college students may also have different effects on college students’ school adjustment, and then lead to different levels of smartphone addiction. As mentioned above, previous studies have explored the grade differences of college students’ meaning in life, school adjustment and smartphone addiction. However, previous studies have seldom explored whether there are grade differences in the relationship between meaning in life, school adjustment, and smartphone addiction.

The present study proposed a moderated mediation model in which school adjustment played a mediating role in the relationship between meaning in life and smartphone addiction and grade played a moderating role in the relationship between meaning in life, school adjustment, and smartphone addiction. Specifically, combining the meaning therapy theory, the meaning in life theory, and the self-determination theory, this study proposed the hypothesis 1: School adjustment plays a mediating role between meaning in life and smartphone addiction among female college students. Based on the theoretical framework of hypothesis 1, this study combined with the identity-based motivation theory to further propose the hypothesis 2: The relationship between meaning in life, school adjustment, and smartphone addiction among female college students is moderated by grade. Figure 1 illustrates the conceptual model of the present study.

The present study was approved by the Research Ethics Committee of Shandong Women’s University. The female college students from 50 classes at five universities in Shandong Province, China, were selected as participants by cluster random sampling in this study. Given the COVID-19 pandemic, the researcher distributed the online informed consent form and online questionnaire to the investigated classes through the Wen Juan Xing platform. First, all participants read the online informed consent form, which included a brief description of the purpose, significance, anonymity, and confidentiality of the questionnaire survey. Then, all participants signed the online informed consent form. Thirty-two participants were excluded for inaccurately completing the measures. Thus, the final sample consisted of 1,076 female college students, including 369 freshmen (34.29%), 379 sophomores (35.22%), and 328 juniors (30.48%). The average age of the subjects was 19.83 (SD = 1.11), and their ages ranged from 18 to 22.

Data were analyzed by using SPSS 26.0 and Mplus7.11 in the present study. The data analysis followed four steps:

First, common method bias analysis was conducted by SPSS 26.0. Specifically, this study used Harman’s One-Factor Test for factor analysis (unrotated exploratory factor analysis) for all items (Podsakoff et al., 2003). Among all factors with eigenvalues greater than 1 obtained after factor analysis, if the variance explained by the first factor is less than 40%, it indicates that there is no common method bias in the study (Podsakoff et al., 2003).

Second, descriptive statistics and Pearson correlation analysis were conducted by SPSS 26.0.

Third, grade was coded with dummy variables and set as the control variable by using SPSS 26.0, and then Mplus7.11 was used to test the mediation model.

Fourth, Mplus7.11 was used to conduct multiple group analysis to test the moderated mediation model. Specifically, this study tested the measurement invariance according to the following four steps: (a) Fit the measurement model separately for each group. (b) Model 1: Configural invariance. (c) Model 2: Metric invariance (common loadings across grade). (d) Model 3: Scalar invariance (common loadings and intercepts across grade). The chi-square statistic, the Tucker-Lewis Index (TLI), the comparative fit index (CFI), and the root-mean-square error of approximation (RMSEA) were used to assess model fit. The criteria for acceptable model are the CFI, TLI > 0.90, the SRMR < 0.05, and the RMSEA < 0.08 (Little, 2013). The chi-square differences between models (p > 0.05) and the differences of model fit (∆CFI < 0.01) were considered as the indications of invariant measurements (Cheung and Rensvold, 2002; Chen, 2007; Hair et al., 2014).

It should be noted that all variables were standardized before testing the mediation model and moderated mediation model. Moreover, both direct and indirect effects were estimated with 95% confidence interval (CI) based on the bias-corrected percentile method with 1,000 bootstrap samples.

Harman’s One-Factor Test was used for factor analysis (unrotated exploratory factor analysis) for all items in this study (Podsakoff et al., 2003). The results showed that the eigenvalues of 18 factors were greater than 1, and the variance explained by the first factor was 23%, less than 40%, which indicated that the common method bias did not exist in the present study.

The means, standard deviations, skewness, and kurtosis (minus 3) of the main variables are presented in Table 1, and the correlation matrix of the main variables are presented in Table 2. The results showed that meaning in life (MIL), school adjustment (SAD), and smartphone addiction (SA) were very approximately normal distribution in the present study. Furthermore, meaning in life was positively correlated with school adjustment (r = 0.51, p < 0.01) and negatively correlated with smartphone addiction (r = −0.50, p < 0.01). School adjustment was negatively correlated with smartphone addiction (r = −0.58, p < 0.01).

As shown in Table 3, meaning in life significantly negatively predicted smartphone addiction (β = −0.28, z = −5.72, p < 0.001) and significantly positively predicted school adjustment (β = 0.50, z = 10.86, p < 0.001), and school adjustment significantly negatively predicted smartphone addiction (β = −0.43, z = −8.81, p < 0.001). The mediating effect of school adjustment was −0.21, accounting for 43% of the total effect, and the 95% confidence interval (95% CI: −0.32 to −0.14) excluded 0. The direct effect was −0.28, accounting for 57% of the total effect, and the 95% confidence interval (95% CI: −0.37 to −0.18) excluded 0. The fit indices of the mediation model showed that χ²(90.384)/df (48) = 1.883, RMSEA = 0.056 (90% CI: 0.034–0.078), TLI = 0.969, CFI = 0.978, and SRMR = 0.033, which all reached the criteria of good model fit.

As shown in Table 4, the measurement model showed an acceptable fit to the data for female freshmen, χ²(df = 32) = 39.626, p < 0.001, CFI = 0.962, SRMR = 0.037, TLI = 0.943, RMSEA = 0.064, for female sophomores, χ² (df = 32) = 46.927, p < 0.001, CFI = 0.941, SRMR = 0.041, TLI = 0.922, RMSEA = 0.073, and for female juniors, χ²(df = 32) = 74.917, p < 0.001, CFI = 0.944, SRMR = 0.039, TLI = 0.925, RMSEA = 0.062. Thus, the measurement invariance tests can be performed next.

Model 1 (configural invariance), model 2 (metric invariance), and model 3 (scalar invariance) all fit well. The model comparison showed that there was no significant difference between model 2 and model 1 in the fit indices (∆χ² = 10.812, ∆df = 14, p > 0.05, ∆CFI < 0.01). Further comparing model 3 with model 2, the result found that there was no significant difference in the fit indices between the two models (∆χ² = 19.839, ∆df = 14, p > 0.05, ∆CFI < 0.01). The above results indicated that the scalar level of invariance (strong invariance) across grade was established for all measures, which satisfied the requirements of structural model comparison.

In order to compare the grade difference of direct effect and indirect effect, the fit indices of the unconstrained structural model (totally free for each group) and the constrained structural model (all the paths equal across groups) were first compared. The results (see Table 5) showed that the fit indices of the unconstrained structural model were good, while those of the constrained structural model were poor. There was a significant difference between the two models (∆χ² = 25.699, df = 6, p < 0.001, ∆CFI > 0.01).

Further comparing the differences of path coefficients among female freshmen (group 1), female sophomores (group 2), and female juniors (group 3), the research results (see Table 6) showed that: (a) There was no significant difference between female freshmen, female sophomores, and female juniors in the path coefficient of MIL→SA. (b) There was no significant difference between female freshmen, female sophomores, and female juniors in the path coefficient of MIL→SAD. (c) The path coefficient of SAD→SA in female juniors was not significant. (d) The path coefficient of SAD→SA in female sophomores was significantly larger than that of female freshmen. (e) School adjustment mediated the relationship between meaning in life and smartphone addiction in female freshmen and sophomores. The mediating effect of school adjustment in female freshmen was −0.22 (95% CI: −0.39 to −0.15), and the mediating effect of school adjustment in female sophomores was −0.39 (95% CI: −0.58 to −0.29). (f) School adjustment could not mediate the relationship between meaning in life and smartphone addiction in female juniors.

Consistent with previous studies (Çevik et al., 2020; Hu et al., 2022), this study found that meaning in life significantly negatively predicted college students’ smartphone addiction. This result is also congruent with meaning therapy theory (Frankl, 1963); that is, the most fundamental drive of human existence is to constantly discover the meaning and purpose of life. Without meaning in life, individuals are likely to fall into a state of emptiness, resulting in some psychological symptoms (Park and Baumeister, 2016; Lin, 2020) and addictive behaviors (Yao et al., 2016; Çevik et al., 2020; Hu et al., 2022). A prior study verified that the higher the level of college students’ life meaning, the less likely they are to have addictive behaviors (Steger and Frazier, 2005). Besides, based on meaning therapy theory, Wang J. J. (2017), Wang X. (2017) found that meaning therapy can significantly interfere with smartphone addiction, further demonstrating that meaning in life is an important factor affecting smartphone addiction. College students may use their smartphones for a number of online activities to escape reality. When college students feel empty and anxious due to a lack of meaning in their lives, they may become addicted to the Internet to escape boredom and release negative emotions, thus leading to smartphone addiction (Hu et al., 2022).

This study further found that school adjustment mediated the relationship between meaning in life and smartphone addiction. This means that a higher level of meaning in life can promote the development of female college students’ school adjustment, in turn reducing female college students’ smartphone addiction; a lower level of meaning in life can hinder the development of college students’ school adjustment, in turn increasing the risk of female college students’ smartphone addiction. In the first path of the mediation process, we found that meaning in life significantly and positively predicted female college students’ school adjustment. This result is congruent with meaning in life theory (Roepke et al., 2014; Glaw et al., 2017; Hooker et al., 2018); that is, a higher level of meaning in life promotes the development of social adjustment. According to the model linking meaning in life to health proposed by Hooker et al. (2018), individuals who have a clear and consistent sense of meaning in life are more aware that their lives are meaningful in their daily interactions with the world, and they tend to better exert self-regulation, feel less daily stress, adopt adaptive coping skills, engage in healthy behaviors, and avoid behaviors that endanger their health. School adjustment is the main component of college students’ social adjustment. Consequently, meaning in life also contributes to college students’ school adjustment. Some empirical studies also support this result. On the one hand, the higher the level of college students’ meaning in life, the less stress, anxiety, and depression they will experience (Park and Baumeister, 2016; Lin, 2020). On the other hand, the higher the level of college students’ meaning in life, the higher their life satisfaction and happiness (McMahan and Renken, 2011; Steger et al., 2011; Lin, 2020). We also found that school adjustment significantly and negatively predicted smartphone addiction in the second path of the mediation process, which is congruent with self-determination theory. The self-determination theory suggests that individuals who satisfy their psychological needs have stronger social adaptability, and their risk of addiction is lower; individuals with frustrated psychological needs may experience less meaning in life, and they are more prone to maladjustment, which may lead them to seek substitutes and compensation in other fields (Deci and Ryan, 2000; Kuzucu and Şimşek, 2013). Smartphones have become essential for college students in their daily lives and studies. Because of its functional characteristics (e.g., collectivity of functions, personalization and customization of content, accessibility, and convenience), smartphones become a tool for college students with school maladjustment to obtain alternative satisfaction and compensation, which easily leads to smartphone addiction (Aker et al., 2017; Boumosleh and Jaalouk, 2017; Kim et al., 2017; Bian et al., 2018; Alinejad et al., 2022). Therefore, based on empirical and theoretical evidence, the above relationship between meaning in life, school adjustment, and smartphone addiction could be well comprehended.

In summary, the present study provided evidence that meaning in life could not only directly affect female college students’ smartphone addiction, but also indirectly affect female college students’ smartphone addiction through school adjustment. According to these results, regardless of grade differences, we can understand that the stronger the meaning in life of female college students, the stronger their overall school adjustment, and the less likely they are to be addicted to smartphones. On the contrary, female college students who lack meaning in life are prone to school adjustment problems. In order to relieve psychological pressure and negative emotions caused by school maladjustment and obtain alternative satisfaction and compensation, they are easily addicted to the “virtual world” of smartphones (Song and Zhao, 2021).

By conducting multiple group analysis, it was found that school adjustment had a partial mediating effect between meaning in life and smartphone addiction for female freshmen and sophomores, while for female juniors, the mediating effect of school adjustment was not significant. The comparison of the grade difference of the paths revealed that there was no significant grade difference in the path coefficients of MIL→SA and MIL→SAD, but there was a significant grade difference in the path coefficient of SAD→SA. The path coefficient of SAD→SA in female sophomores was significantly larger than that of female freshmen. According to identity-based motivation theory (Oyserman, 2009a,b), people will behave in a way that is consistent with the identity initiated in a certain situation. But this kind of “identity” is not stable, and it will change with the change of external environment. In different grades, college students need to face different external environmental challenges. Adapting to the university quickly is a major challenge for freshmen (Lu, 2015; Zhang Y. L. et al., 2017; Zhang Y. et al., 2017). After entering the university, freshmen are full of passion and expectation for the upcoming university life, and they actively adjust themselves to adapt to the university life (Lu, 2015). Besides, college teachers pay more attention to their study, life, and mental health (Zhang Y. L. et al., 2017; Zhang Y. et al., 2017). All of these help them to form their possible selves which are in line with the school environment requirements of freshman year, and then promote the formation of their healthy identities. Thus, female freshmen’s meaning in life is the highest compared with other grades in this study (see Table 1), which is consistent with the results of previous studies (Zhang and Zhou, 2020; Xie, 2021). The high level of meaning in life helps them to develop good school adjustment, in return reducing the possibility of their smartphone addiction. Sophomores formally enter the stage of autonomous learning, and their learning pressure in specialized courses has further increased (Gahagan and Stuart Hunter, 2008; Sanchez-Leguelinel, 2008). They do not feel so fresh about college life any more, and they start to lose interest in it (Richmond and Lemons, 1985; Lu, 2015; Zhang Y. L. et al., 2017; Zhang Y. et al., 2017). Besides, after the students enter the sophomore year, the degree of attention paid by teachers to them is reduced, which easily leads to many students’ depressions and problems in their study and life (Lu, 2015; Zhang Y. L. et al., 2017; Zhang Y. et al., 2017). The above phenomenon among sophomores is called the “sophomore slump” by scholars. Obviously, sophomores need to face very severe challenges. Under the influence of the above-mentioned internal and external unfavorable factors, sophomores may form negative possible selves, which may conflict with the school environment requirements (developing autonomous learning ability) of sophomore year, leading to their “identity crisis” (Li and Liu, 2010). As a result, female sophomores’ meaning in life is seriously lower than that of their freshman year in this study (see Table 1), which is consistent with the results of previous studies (Zhang and Zhou, 2020; Xie, 2021). The low level of meaning in life may lead to their serious school maladjustment, further leading to serious smartphone addiction. Consequently, it can be easily understood that compared with freshmen, sophomores are more prone to smartphone addiction due to school maladjustment. Compared with freshmen and sophomores, entering a higher school and employment are the main stressors for juniors (Lu, 2015). Under the influence of these pressures, juniors have to make great efforts to cope with the challenges of entering a higher school or employment. They began to reflect on their sophomore life and study, think about their life direction, and adjust their behaviors to truly adapt to the university (Zeng and He, 2015). In short, juniors are developing in the direction of forming a healthy identity. Therefore, consistent with the results of previous studies (Zhang and Zhou, 2020; Xie, 2021), female juniors’ meaning in life is higher compared with female sophomores in this study (see Table 1), which contributes to the development of their school adjustment. In addition, since entering a higher school and employment have replaced school adjustment as the main stressors of juniors, the pressures of entering a higher school and employment are probably the inducing factors that leads to female junior students’ smartphone addiction, while the pressure of school adjustment is not. Thus, it is easy to understand meaning in life could not affect female juniors’ smartphone addiction through school adjustment.

To sum up, the relationship between meaning in life, school adjustment, and smartphone addiction was moderated by grade. For female freshmen, the high level of meaning in life promotes the development of their school adjustment, thus reducing their risk of smartphone addiction. For female sophomores, the low level of meaning in life may lead to their school maladjustment, thus increasing their risk of smartphone addiction. For female juniors, meaning in life could not mediated the relationship between meaning in life and smartphone addiction.