Based on the above rationale and identified gaps, the present study addressed the following research questions and hypotheses.

Using a cluster sampling method, questionnaires were administered to students from Grades 6 to 8 at a junior high school. The survey included the Emotional Security Scale, the revised Inventory of Parent and Peer Attachment (IPPA-R), and the Center for Epidemiologic Studies Depression Scale (CES-D). A total of 450 questionnaires were distributed, and 446 were returned. After removing 10 incomplete responses, 436 valid questionnaires were retained, yielding an effective response rate of 96.89%. Among the participants, 219 were boys and 217 were girls; 148 were in Grade 6, 142 in Grade 7, and 146 in Grade 8.

The study protocol was approved by the Institutional Review Board of Ludong University (Approval No. LDU-IRB2025140007) and complied with the Declaration of Helsinki. Written informed consent was obtained from all participants and their custodial authorities prior to data collection. Participants were informed that participation was voluntary and that they could withdraw at any time without penalty. To protect confidentiality, all data were de-identified using unique codes, stored on password-protected devices, and accessed only by the research team; any potentially identifying information was removed from reports. Given the assessment of depressive symptoms, a risk-management procedure was implemented: students indicating elevated depressive severity or potential self-harm risk were promptly referred to the school mental health professional and, when necessary, their guardians were notified in accordance with school policy and safeguarding requirements.

All data were coded and analyzed using SPSS 22.0. Statistical analyses included reliability testing, common method bias assessment, and correlation analyses among emotional security, interpersonal trust, and depressive tendencies.

Based on the questionnaire results from Study 1, six participants with interpersonal trust scores below 35 and depressive tendency scores above 20 were screened. With the consent of the participants and their families, one 14-year-old female student (referred to as Participant A) and her parents were selected for the intervention study. Study 2 was conducted under IRB approval from Ludong University (Approval No. LDU-IRB2025140007). One student and the student’s parents (family sessions) provided written parental consent and student assent; participation was voluntary and families could withdraw at any time. Data and sandtray records were de-identified and securely stored with restricted access. Depressive-symptom risk was monitored, and any safety concerns prompted referral to school mental health services and supervisor consultation, with guardian notification per school policy.

Participant A was an only child in the third year of junior high school. Her parents frequently argued, and these conflicts often involved her. She exhibited strong feelings of self-loathing and guilt, believing that her parents’ marital discord was her fault and that their lives would improve if she disappeared. During the 2 weeks prior to the intervention, she reported severe insomnia, depressed mood, loss of interest, declining academic performance, and interpersonal difficulties accompanied by school aversion.

A single-subject experimental design was adopted (A–B–A format). The first A phase represented the baseline stage (A1), B represented the intervention stage, and the second A represented the follow-up stage (A2).

Baseline Phase (A1): From May 16 to May 23, 2022, the IPPA-R and CES-D were administered twice prior to the intervention to obtain a stable baseline for comparison with post-intervention data.

Intervention Phase (B): From May 28 to July 18, 2022, eight sessions of sandplay therapy were conducted under the guidance of The Clinical Practice of Sandplay Therapy (Zhang, 2012). Data were collected after each session. The same measurement tools, time frame, and environment were maintained as in the baseline phase to compare changes in interpersonal trust and depressive tendencies before and after the intervention.

Follow-up Phase (A2): From August 29, 2022, to February 13, 2023, six follow-up assessments were conducted using the same measurement tools. Data collected during this phase were used to examine the sustainability of the intervention effects.

This study examined the relationship between emotional security and depressive tendencies among junior high school students and explored the mediating role of interpersonal trust. Results showed that emotional security negatively predicted depressive tendencies, with interpersonal trust serving as a partial mediator.

Consistent with previous findings (Geng et al., 2021), emotional security was a significant negative predictor of depressive tendencies. Emotional security arises from experiences of parental conflict; thus, adolescents exposed to frequent family conflicts are prone to negative emotions and psychological dysregulation (Davies and Cummings, 1998). Persistent exposure to such conflict consumes psychological resources needed for self-regulation, increasing the risk of depression (Jiang et al., 2025). Compared with studies that focus primarily on family conflict frequency or other distal family risk indicators, the current results underscore emotional security as a psychologically proximal factor linked to adolescents’ depressive tendencies, which may help clarify how family climate translates into emotional outcomes.

Interpersonal trust mediated the relationship between emotional security and depressive tendencies. Emotional security positively predicted interpersonal trust, aligning with prior research (Li et al., 2025). According to attachment theory, early emotional connections shape internal working models that influence how individuals perceive self-worth, intimacy, and social interactions (Fearon and Roisman, 2017). Positive family emotional interactions strengthen children’s sense of safety and form the basis of trust toward others (Li et al., 2025). Conversely, repeated family conflicts undermine emotional security, leading to trust crises in social interactions—a pattern confirmed across cultures (Szcześniak et al., 2012). Moreover, interpersonal trust negatively predicted depressive tendencies (Zeng and Xia, 2019). The stress generation model (Hammen, 1991) posits that individuals with depressive vulnerability tend to perceive and respond to stressors passively, reinforcing negative cognitive schemas. Adolescents with low interpersonal trust may avoid social interactions and experience emotional detachment, increasing vulnerability to depression (Jiang et al., 2021). In contrast, those with higher levels of trust can better perceive care and support from others, accumulate psychological resources, and thereby mitigate depressive symptoms (Grace and Schill, 1986). Notably, interpersonal trust functioned as a partial rather than full mediator, suggesting that emotional security may also influence depressive tendencies through additional pathways (e.g., emotion regulation, maladaptive cognitions, or peer-related stress processes). This pattern is consistent with multi-process accounts of adolescent depression and highlights the need to model both relational and intrapersonal mechanisms in future research.

By specifying interpersonal trust as a relational mechanism, the current model moves beyond documenting family risk and identifies a modifiable social–cognitive pathway through which emotional security may shape adolescents’ vulnerability to depressive tendencies. This extends prior research by clarifying not only whether these variables are associated, but also how family emotional climate may be translated into downstream socio-emotional outcomes during early adolescence.

Based on toy coding and linguistic analysis (Roesler, 2019; Turner, 2023), changes observed across the ABA phases suggest that the combined individual and family sandplay procedures were associated with improvements in interpersonal trust and reductions in depressive tendencies at the case level. In addition, family sandplay sessions provided observable shifts in interaction patterns that were consistent with improvements in parent–child communication and trust. Given the single-case nature of the design, these findings should be interpreted as preliminary and descriptive rather than conclusive evidence of efficacy. Individual sandplay sessions provided clearer insights into changes in depressive symptoms, whereas family sandplay sessions offered more direct observations of changes in interpersonal trust. This distinction aligns with theoretical perspectives suggesting that individual sandplay better reflects unconscious processes, while group or family sandplay is more effective in observing and improving interpersonal interactions (Turner, 2023). Participant A’s scores for interpersonal trust and depressive tendencies showed a fluctuating but overall positive trend across the baseline, intervention, and follow-up phases—particularly during sessions 3–4 of the intervention and sessions 2–3 of the follow-up. These fluctuations may be associated with stressful life events experienced prior to therapy. From a comparative perspective, this pattern is consistent with clinical process accounts in which emotional activation and symptom fluctuation can occur when distressing material emerges and is processed, before more stable improvements are consolidated.

Therefore, sandplay therapy can serve both as an intervention tool for improving trust and reducing depressive states, and as a preventive, school-based risk assessment tool for relationship and emotional difficulties. In practice, the combined use of individual and family sandplay may be particularly valuable in school settings: individual sessions can facilitate affect expression and self-representation, whereas family sessions can externalize interaction patterns (e.g., fragmentation vs. coordination; conflict vs. cooperation) and provide opportunities to practice communication and trust-building in vivo. Nevertheless, further replication with larger samples and controlled designs is required to strengthen generalizability and causal inference.

Relative to prior sandplay studies that focus on either individual or group formats, Study 2 adds value by combining individual and family modalities and documenting phase-based process markers of trust/communication and interactional organization in a school-based setting, thereby providing a more clinically informative picture of how relational change may unfold over time. These case-level process indicators (toy themes and reflection language) provide descriptive evidence that is broadly consistent with the correlational mediation pattern observed in Study 1. However, given the single-case ABA design, this qualitative information should be interpreted as complementary process data rather than confirmatory evidence of efficacy.

The present study contributes to the literature in three ways. First, it integrates family-based emotional security with a relational mechanism—interpersonal trust—to explain depressive tendencies in early adolescence, thereby extending prior work that typically examines these constructs in isolation. Second, the finding of partial mediation suggests a multi-pathway process in which family emotional climate shapes adolescents’ internal sense of safety and simultaneously influences broader social expectations and relational engagement, offering a more process-oriented account of how family experiences translate into emotional outcomes. Third, by combining individual and family sandplay and documenting process markers (e.g., miniature themes related to communication/trust and shifts in spatial organization and interaction), the study provides descriptive evidence on how relational meanings may be externalized and reorganized through symbolic play in a school-based context.

Practically, the findings suggest several implications for school-based mental health services. First, assessment and intervention efforts may benefit from targeting adolescents’ sense of emotional security and interpersonal trust simultaneously, particularly for students exposed to family conflict. Second, the combined use of individual and family sandplay may be clinically useful: individual sessions can facilitate the expression of internal emotional states, whereas family sessions can make interaction patterns visible and provide opportunities to practice communication and coordination in vivo. Third, the observed process indicators (e.g., emergence of trust/communication-related miniatures, increased integration of the overall scene, and reduced fragmented placement) may serve as qualitative signals to guide case formulation and monitor change. Finally, because school-based delivery may introduce peer attention or labeling effects, implementation should prioritize privacy protection and minimize unintended social exposure.

The findings should also be interpreted in the Chinese school context, where academic evaluation and high-stakes examinations may intensify stress and shape adolescents’ emotional functioning and help-seeking. In addition, culturally embedded family communication norms and concerns about stigma/privacy may influence both interpersonal trust and participation in school-based counseling, which should be considered in implementation.

From a school-based prevention perspective, brief screening of emotional security, interpersonal trust, and depressive tendency may help identify students who could benefit from early support. Schools may combine universal psychoeducation on emotion regulation and trust-building communication with targeted referral to counseling for at-risk students, while ensuring privacy-protective procedures to reduce labeling effects.

First, the study sample primarily included students from Grades 6 to 8, excluding Grade 9 students who often experience heightened stress due to high school entrance exams, potentially limiting generalizability. Because Grade 9 students face markedly different academic demands and time pressure, the strength and nature of the associations among emotional security, interpersonal trust, and depressive tendencies—as well as responsiveness to school-based interventions—may differ in this group. Future research should explicitly include Grade 9 students and consider stratified sampling or comparing cohorts across key time points (e.g., beginning of term, pre-exam, and post-exam) to examine whether exam-related stress moderates these relationships and intervention effects.

Second, since the sandplay intervention was conducted in a school counseling room, participants’ frequent visits drew attention from peers, which may have influenced their creations. This visibility may have introduced labeling and reactivity effects (e.g., heightened self-consciousness, social desirability, or demand characteristics), which could influence both self-report ratings and sandtray productions. In the present study, sessions were conducted in a private counseling room and confidentiality was emphasized; however, complete concealment of participation in a school setting was not feasible. Future studies should further reduce visibility by scheduling sessions at low-traffic times, using more discrete access procedures, or integrating sandplay activities into universal or classroom-based formats (e.g., whole-class participation) to minimize labeling and peer attention.

Finally, although the study adopted a single-case ABA design (baseline–intervention–withdrawal/follow-up) to strengthen within-participant comparisons, the findings are still limited by the single-participant nature and the constraints inherent to ABA designs. In particular, intervention effects may carry over into the withdrawal/follow-up phase, and observed changes may also be influenced by maturation, history effects, or other concurrent events; therefore, causal conclusions and generalization beyond the case should be drawn cautiously.

Additionally, Study 1 used a cross-sectional design; therefore, the observed associations and the mediation model should be interpreted as correlational/statistical (i.e., an indirect effect) rather than causal, and directionality cannot be established. Longitudinal or experimental studies are needed to test causal pathways among emotional security, interpersonal trust, and depressive tendencies.

Future research should expand the sample to include Grade 9 students and examine the dynamic effects of academic stress on emotional wellbeing across different time points (e.g., beginning of term, pre-exam, post-exam). Intervention settings should also be improved to reduce labeling effects—for example, by integrating sandplay into naturalistic classroom activities or adopting whole-class participation designs.

Methodologically, future studies could combine experimental interventions with cross-lagged models, incorporating family functioning and peer support as ecological variables to build a multilevel causal framework.