In total, 69 children (43 male) from four German kindergartens, all born in Germany, who ranged in age from 3;0 to 4;8 years (M = 4.12, SD = 0.54) at the time of their initial assessment, participated in the present longitudinal study. In Germany, about one third of the children younger than 3 years and about 90% of the children aged between 3 and 6 (maximum 7) years attend a kindergarten (Statistisches Bundesamt, 2012), the majority of them from morning to late afternoon, including lunch.

The participating four kindergartens each have several kindergarten groups, more or less mixed in age, with several teachers minding a group of 10 to 25 children. These kindergarten groups are not considered as fixed “classes,” however, they were kept constant during the period of data collection. As standard in Germany (Niklas and Schneider, 2013), there was no formal reading and writing instruction provided in any the participating kindergartens.

Four samples of children, one from each of the four participating kindergarten centers, were created in a way that these did not differ statistically in mean age, age-range from 3 to 4 years, gender, mean time spent in kindergarten per week, number of books for children and adults in household (note that in the literacy enrichment group the number of books in household, except children books, even though being about twice as high as in the other groups, did not differ significantly; two parents from this group held an exceeding collection of dime novels), preferred leisure time activities (e.g., TV watching, computer gaming, playing outside), frequency of visiting public libraries (see Tables 1, 2 for details), and, most important, in SES (family income, school-leaving qualification and professional situation of the parents; see Table 2). These factors were evaluated using a family socio demographic questionnaire (Simon and Sachse, 2013) completed by all parents before the data collection. The majority of the parents in our study had high or medium school level qualification and a family net income of more than 2000 Euros per month (see Table 2), which both is comparable to the total population in Germany (59 and 54%, German Federal Statistical Office, 2016).

The authors received Institutional Review Board Approval for this study. The study was carried out in accordance with the recommendations of The German Society of Psychology, with written informed consent from the parents of all children. All parents gave written informed consent in accordance with the Declaration of Helsinki. The protocol was approved by the administration of the City of Kaiserslautern, Council for Youth and Sports. Each of the four samples was randomly assigned to serve as one of the three shared book reading intervention groups (experimental groups): (1) Method 1 = literacy enrichment group (N = 13); (2) Method 2 = teacher training group (N = 18); (3) combination group: Method 1 and 2 combined (N = 17); or as the control group: none of the methods were applied until post-test (N = 21). See Table 1 for sample description.

The literary enrichment group and the combination group, each acquired 100 additional different storybooks in order to establish a library system. The storybooks were chosen according to their potential to support vocabulary growth (following guidelines and suggestions by stiftunglesen.de; kinderbuch-couch.de; kidsbestbooks.com; lesestart.de) with colorful pictures and related text on each single page, in order to support emergent literacy. Each of these storybooks was registered with a code and positioned within easy reach of the children. A letter was sent to all parents in which they were informed about the availability of these books and encouraged to read them with their children at home “as often as possible.” Managed and controlled by a graduate student, once a week the children could borrow a new book after bringing back the one borrowed the week before. This procedure was chosen in order to acquaint the children with library rules. There was, however, no financial consequence or any kind of punishment if the book was lost or damaged; borrowing a new book was still possible. Children were free to choose any storybook; the graduate student did not pressure nor make any suggestions. In order to inform the parents, each child received a form with their name and the date when the book was borrowed and when it should be returned.

For teacher training (Method 2), formal instruction was given to the teachers of the two groups for which this method was applied, the teacher training group and the combined group, using one component of the Heidelberger Interaktionstraining für pädagogisches Fachpersonal zur Förderung ein- und mehrsprachiger Kinder – HIT (Buschmann and Jooss, 2011), namely shared book reading. The goal of the training, which integrates dialogic reading techniques, is to directly increase the opportunities for children’s language development through shared book reading. Dialogic reading is an intervention approach, originally developed by Whitehurst et al. (1988), that involves high levels of adult–child language interactions during book reading. The program follows three main principles: (a) encouragement of the child to participate, (b) provision of feedback to the child, and (c) adaptation of the adult’s reading style to the child’s language ability. The child is supposed to be active while the adult is reading; the child learns to become a storyteller.

An important part of the teacher training program is that teachers learn to select the right storybook for optimal shared book reading activities. The storybooks should, according to the authors, contain colorful illustrations with related text at each single page. The illustrations should motivate to interactive communication. In order to foster this, the topic of the storybook should meet the interest of the child and the text should include terms and concepts appropriate to the level of her/his cognitive development.

Sixteen teachers completed the teacher training (teacher training group, N = 7; combined group, N = 9). The training was conducted by a professional instructor, one of the authors of HIT (Buschmann and Jooss, 2011), for a total charge of €3,900 Euros. In order to control for the quantity and the quality of the instruction between the groups, the teachers of both groups were randomly assigned to two mixed training classes. The shared book reading training was conducted in three sessions of four 1-h lessons each with an interval of 1 month between each session. At the end of each session, the teachers received written material (about 10 pages including pictures) in an understandable and motivating form with a synopsis of the strategies learned at the sessions (cf. Buschmann and Jooss, 2011). The training sessions were conducted in a seminar room at the University of Kaiserslautern. The training contained verbal instructions, video demonstrations, model learning, and joint elaboration of activities. Additionally, at the end of the final session coaching was offered, i.e., before session 3 the participants were asked to apply what they had learned in practice and to videotape their shared book reading activities for professional supervision and feedback. Four digital video cameras (two per group) were provided for this purpose.

The teachers were instructed to apply the dialogic book reading strategies three to four times a week in a 1:1 manner, i.e., with one child at time, for approximately 15 min per child, in a quiet room. Each teacher was in charge of three to four children. The teachers used storybooks available in the classroom book corners, if they were in accordance with what they have learned in the training about the selection of storybooks (see above). This holds also for the combination group, i.e., the books provided additionally to this group (Method 1) were not used for Method 2.

In reading logs, for every day (Monday–Friday), each teacher marked her/his frequency of shared book reading activities with each of the three to four children she/he was assigned to. Both kindergartens were visited weekly to collect the logs, to check compliance and to provide guidance.

The control group did not participate in any special instruction or activity. At the end of the study this kindergarten received €300 worth of books as a thank-you gift.

In order to measure expressive vocabulary in preschool age before and after shared book reading intervention, a subtest of the Revised Vocabulary Test for 3- to 5-year-old Children (“Aktiver Wortschatztest für 3- bis 5-jährige Kinder – AWST-R 3-5”; Kiese-Himmel, 2005) was used. Children were instructed to look at a picture and to verbalize what they saw and what action could be described by asking them “what is it” (“Was ist das?”) – for vocalization of substantives, or “what are they / is she / he doing” (“Was macht sie/er…?”) for verbalization of verbs. According to the tests manual, one point was given for each correct answer. The total of 74 items was divided in two parallel forms of 37 items each. The two forms had equal difficulty. One version was used for pre-testing and the other for post-testing. The pictures were presented on the screen of a laptop computer.

In order to measure grapheme awareness, we developed a task which tested children’s familiarity with grapheme forms. In each of 10 trials they had to identify a grapheme presented amongst three non-letter distractors displayed simultaneously on the computer screen, by pointing to it without having to name it. Thus, the test could be applied before formal instruction on grapheme–phoneme conversion rules. For each of these 10 trials a display with four items was presented individually. Each display consisted of one upper case letter and three distractors: one pseudo-letter, one number, and one symbol, each presented in varying location either in the upper left/right, lower left/right part of the screen. All distractors looked similar to letters and may even be used in text (symbols and numbers). Thus, the task required more than just an idea how readable material looks like (Bialystok, 1995), it rather requires familiarity with concrete forms of a real graphemes. The letter items were D, M, W, P, G, H, S, K, F, R, deformed versions of them served as pseudo-letters. Further ten symbols from regular keyboards (e.g., #, $, %) and the ten first numbers (e.g., 1,2,3) were used as distractors.

The question given orally to the children after the onset of each trial was “where is the letter” (“Wo ist der Buchstabe?”). For each correct answer, the child received one point. The chance level was 25% in total. Considering a 95% confidence interval for chance level a score up to 4 must be considered as within chance level. Four children in the combination and the control group, respectively, and two children in the literacy enrichment and teacher training group, respectively, reached a score higher than this. These frequencies do not differ between the groups, χ²(3) = 1.02 (p = 0.80).

The duration of conducting both tests together (first expressive vocabulary, measured with a subtest of the AWST-R 3–5, followed by the grapheme awareness task) did not exceed 30 min. After 6 months intervention time, these two tests, were repeated in the posttest section.

We registered parameters of compliance in order to test whether the effects of both methods is influenced by the frequency of which children were exposed to shared book reading. Literacy enrichment group and the combination group were comparable regarding the number of borrowed books, frequency and length of shared book reading with a parent, number of books forgotten to return, and frequency of children’s absence from kindergarten (see Table 3). Regarding teacher training group no difference between the teacher training group and the combined group in the frequency of absence of teachers and children was found. The higher frequency of teacher–child shared book reading in the combination group as compared to the teacher training group did not reach significance after Bonferroni correction (see Table 3).

Knowledge for letters which are part of the child’s first name has been shown to be enhanced in some studies (Treiman and Broderick, 1998). To rule out corresponding biasing effects on the grapheme awareness task, χ² tests were performed to check whether the frequency of the target letters of this task is comparable within the prenames of the children for the four groups. The occurrence of the target letters within the prenames was comparable in all four groups, χ²(3) = 7.00 (p = 0.86). Moreover, the occurrence of the target letters as the first letter of the prename was comparable in all four groups, χ²(3) = 4.09 (p = 0.25). There were no correlations between the number of target letters within the own prename and the performance in the grapheme awareness pretest, r < 0.01 (p > 0.99), and posttest, r = -0.03 (p = 0.83), indicating that the results of the grapheme awareness task were not influenced by the occurrence of the target letters in the children’s first names.

AWST-R scores (expressive vocabulary as measured by the number of correct words in the AWST-R 3-5) and grapheme awareness scores (number of correct letters in the letter recognition task) were analyzed including the factors Time (before vs. after the intervention) as within-participants factor, and Group (Library Group, Teacher Training Group, Combination Group, Control Group) as between-participants factor. Since these dependent variables were associated (AWST-R Pretest with grapheme awareness Posttest: r = 0.32, p < 0.01; AWST-R Posttest with grapheme awareness Posttest: r = 0.29, p = 0.02) a multivariate analysis of variances (MANOVA) was run first, followed by univariate ANOVAS of each dependent variable. Partial eta squared and Cohen’s dz (Cohen, 1988) are reported as measures of effect size.

The Box’s M test revealed homogeneity of the covariance matrices, χ²(30) = 20.33 (p = 0.91). In line with this finding, the Levene test revealed homogeneity of variances between groups for both, the AWST-R, F(3,65) = 0.30 (p = 0.83), and the grapheme awareness task, F(3,65) = 0.30 (p = 0.82).

Since Kolmogorov–Smirnov tests revealed that grapheme awareness scores were not normally distributed (p < 0.01, for the data at both time points), for post hoc analyses of this dependent variable we additionally used bootstrapped t-tests, appropriate for data not normally distributed (Bollen and Stine, 1990; Preacher and Hayes, 2004).

The MANOVA revealed a main effect of Group, Wilk’s λ = 0.76 (p < 0.01, ηp2 = 0.13), a main effect of Time, Wilk’s λ = 0.46 (p < 0.01, ηp2 = 0.54), and an interaction between Time and Group, Wilk’s λ = 0.78 (p = 0.01, ηp2 = 0.12). Significant improvements over time were found for all groups, all ts < -2.75 (ps < 0.01), with the exception of the control group, t(20) = -0.93 (p = 0.35).

The ANOVA on the AWST-R scores revealed a main effect of Time, F(1,65) = 30.66, p ≤ 0.01, ηp2 = 0.32, with a higher performance for the second compared to the first time point, t(68) = -5.54, p ≤ 0.01. Moreover, there was a main effect of Group, F(3,65) = 3.65, p = 0.02, ηp2 = 0.14. The Library Group achieved higher scores compared to all other groups, all ts ≥ 2.74, p ≤ 0.01, whereas no differences were found between the remaining three groups, all ts ≤ 0.09. There was an interaction between Time and Group, F(3,65) = 2,73, p ≤ 0.05, ηp2 = 0.11. A significant improvement over time was found for all intervention groups, all ts ≥-2.48, ps ≤ 0.016 (Library Group: dz = 0.75; Teacher Training Group: dz = 1.38; Combination Group: dz = 0.63). No difference over time was found for the Control Group (see Figure 1).

For the second dependent variable, scores in the grapheme awareness task, ANOVA revealed a main effect of Time, F(1,65) = 32.26, p ≤ 0.01, ηp2 = 0.33, with a higher performance for the second compared to the first time point, t(65) = -5.68, p ≤ 0.01. For the main effect of Group, F(3,65) = 2.60, p = 0.06, ηp2 = 0.11, and the interaction between Time and Group, F(3,65) = 2.55, p = 0.06, ηp2 = 0.11, there was a clear tendency (6% level), i.e., statistical significance at the 5% Level was narrowly missed. The scores of grapheme awareness were, as mentioned before, not normally distributed. Therefore, additional bootstrapped confidence intervals were conducted (Bollen and Stine, 1990; Preacher and Hayes, 2004). These analyses revealed that all groups, with the exception of the Control Group, improved significantly over time (see Figure 2). For detailed results of the bootstrapped t-tests, see Table 4.

Results from the literacy enrichment group show that simply providing a large number of adequate books to children, followed by an informal encouragement of the parents to read these books with the children at home, improves children’s language development in terms of expressive vocabulary. It seems that the availability of appropriate books in an educational institution connects home and school activities in favor of language development by stimulating literacy activities at home (Wade and Moore, 1996; Deunk et al., 2013): supporting children to experience of the “intimacy” of shared reading in home settings (Merchant, 2008) and making “recreational reading” part of the routine (Morrow and Weinstein, 1986). In fact, many parents expressed their gratitude for the opportunity for their children to borrow good books. Some, for instance, created a special bag for the home–school book transport. It seems that this method simply encourages families’ participation in shared book reading activities (Meyer et al., 2015).

This “opportunity invites” principle seems also to hold true for the children themselves, who were highly motivated to choose a new book each week. Some of them were talking about their expectations regarding the borrowed book or, when returning the book, they judged it, discussed the content and told us whether or not they liked it. Borrowing books may have attracted and increased children’s general attention to books. Such effects have been reported in the literature (Robinson et al., 1996). Moreover, with the frequent use of the borrowing method, children may have acquired skills in how to deal with the wide variety of books, as usually found in public libraries, and have learned how to choose a book that meets their subject expectations (Hurrelmann et al., 1993; Deunk et al., 2013).

The text and pictures of the storybooks used in the present study were optimal for retaining children’s attention and for stimulating language development (stiftunglesen.de; kinderbuch-couch.de; kidsbestbooks.com; lesestart.de), with colorful pictures and related text on each single page, whereas many books which children usually have at home are not of the same standard (Elliott and Hewison, 1994; Marsh, 2003). Thus, literacy enrichment does not only increase the quantity of shared book reading activities but also its quality.

Altogether, we can conclude that literacy enrichment is an effective method which can, due to relatively low costs and without financial liability for the parents, easily be implemented in kindergarten centers. Only one single book out of the 200 we sponsored for literacy enrichment was considerably damaged and only five books were not returned. At the end of the study, the remaining books were still available to all children of the two kindergarten groups.

Results from the teacher training group show that providing formal shared book reading instruction (Method 2) results in positive effects on children’s expressive vocabulary, corroborating the findings of other studies which found similar results of different formal teacher training instruction (Valdez-Menchaca and Whitehurst, 1992; Wasik and Bond, 2001; Buschmann and Jooss, 2011; Simon and Sachse, 2013; Milburn et al., 2014). As a consequence of the training, teachers learned the importance of open questions, how to do corrective feedback, how to use expansions and how to motivate children to speak and to be more active during telling the story. This seems to increase both quantity and quality of shared book reading activities (Whitehurst et al., 1988) and its subsequent impact on language development.

Moreover, teachers learn how to create a scenario for incidental vocabulary learning, which means the development of word knowledge may occur through natural contexts that differ from formal teaching (Valdez-Menchaca and Whitehurst, 1988). In such incidental context through shared book reading, children are exposed to an unstructured rich meaningful environment that can be accessed via language, and the process of acquiring some knowledge is based on children’s spontaneous interest, and not followed by a preselected sequence of topics (Valdez-Menchaca and Whitehurst, 1988). After the child has expressed interest in some subject or aspect of the story (it could be verbally or non-verbally), the teacher can interact by requiring and helping the child to verbalize their thoughts in the context of the story.

Results of the combination group showed that combining the two methods of shared book reading results in positive effects on children’s expressive vocabulary. This matches finding by Mason et al. (1990) and Whitehurst et al. (1994) which showed similar effects of combining shared book reading at home and at kindergarten in children’s language development.

The effect of combining the two methods was, however, not higher when compared to the effects of the methods applied alone, respectively. This may be considered as somewhat surprising, because in this group both methods were applied to the same extent as in the other two groups, respectively, and children were thus exposed to considerably more frequent shared book activities. It seems that effects of shared book reading reached a ceiling effect, i.e., the effect increased with an increase in quantity (Ehmig and Reuter, 2013), however, only to a certain level, and after threshold, cannot be improved further by quantity.

Results from the literacy enrichment group show positive effects on grapheme awareness. In earlier studies, effects of various shared book reading activities on letter knowledge were shown (Ezell and Justice, 2000; Aram, 2006; Piasta et al., 2012). In these studies, however, explicit letter instruction was given. Children were, for instance, asked to verbalize the letter names or to point to the requested letter (Sénéchal et al., 1998; Ezell and Justice, 2000). The present results show that even without explicit letter instruction, shared book reading may implicitly help children to become aware of the difference between printed letters and other visual configurations (Goodman, 1986; Robins et al., 2012). This awareness was measured by the ability to identify a grapheme within a set of items including three non-letter distractors, which all looked similar to letters and may even be used in text. Thus, the task requires more than just an “idea how readable material looks like” (Bialystok, 1995), it rather requires familiarity with definite forms of existing graphemes (including their orientation and detailed features), i.e., the awareness that the chosen item represents a real grapheme. We termed this awareness “grapheme awareness.”

The finding that shared book reading increases grapheme awareness is of practical importance because, for German kindergarten children formal letter instruction is not part of the pre-school curriculum. Many children enter Grade 1 (after reaching the age of six) with only little knowledge about letters and without reading ability (Mann and Wimmer, 2002; Niklas et al., 2011). In contrast, US kindergartens, for instance, usually offer activities that encourage learning the letter names and their sounds with activities that require giving pre-reading attention to the phonological segments of words (Mann and Wimmer, 2002). Such cultural differences were also reported for home literacy activities (see Lego Learning Institute, 2003, for an overview). Literacy enrichment can easily be implemented and may help German kindergarten children to be better prepared for learning to read and write in school.

Whereas the effects of literacy enrichment on expressive vocabulary has been discussed in the literature extensively, effects on grapheme awareness were not addressed so far. In the following, we will discuss how the positive effects we have found could be explained.

We observed that when children borrowed a book, they usually first checked its content before making a decision in favor of one. Related activities, such as choosing some books from the bookshelf, exploring and handling them, putting the chosen one in and out of the satchel, etc., provide additional opportunities for contact with written text.

The books from the literacy enrichment method were managed by an external person (research assistant from our lab). In principle, however, this could also be managed by the teachers without taking away too much time from the other activities (Morrow and Weinstein, 1986; Robinson et al., 1996). In fact, when teachers organize the borrowing, it is already part of reading related interaction; teachers can help children to choose a book by talking about the title or the expected content (Deunk et al., 2013), and in the end it is more likely that the child will like the book.

Results from the teacher training group showed a positive effect of the training program on children’s grapheme awareness, even though the program is focused on strategies of expressive language development. It seems, children have still been supported to informally learn how print looks and thus to acquire familiarity with the visual characteristics of the letters and their orientation (Lachmann and Geyer, 2003; Robins and Treiman, 2009; Neumann et al., 2013; Both-de Vries and Bus, 2014).

Results of the combination group showed that combining the two methods of shared book reading results in positive effects on grapheme awareness. Even though the effect size for this group was considerable larger than for the groups in which the methods were applied alone, there was no statistical evidence for a difference. Therefore, the finding is identical to what was found for expressive vocabulary. Here too, this may be considered as surprising, because in the combination group both methods were applied to the same extent then in the other two experimental groups, respectively, and children were thus exposed to considerably more frequent shared book activities. As discussed for expressive vocabulary, here too, it could be that the effect of shared book reading on grapheme awareness increases with quantity, but only up to a certain level.

We conclude that both methods, literacy enrichment and teacher training trigger experiences with print through shared book reading even without formal letter instruction (Sonnenschein and Munsterman, 2002; Sawyer et al., 2014). Thereby children begin to distinguish letters from other visual configurations and, consequently, will learn that letters are symbols representing language elements and to visually perceive and process graphemes analytically. This modification of visual perception is considered to be an important precondition of literacy development, in particular to learn grapheme–phoneme correspondences (Lachmann, 2002; Lachmann et al., 2012; Lachmann and van Leeuwen, 2014). This is not restricted to transparent orthographies, such as German (Ehri, 1998; Lachmann et al., 2010).

To the best of our knowledge the present study is the first one in which the effect of shared book activities without letter instruction on grapheme awareness is measured. For gaining letter knowledge, i.e., for learning the grapheme-to-phoneme conversion rules in the alphabetic phase of literacy acquisition (Frith, 1985), the children have to process graphemes differently than similar non-letter configurations (Lachmann and van Leeuwen, 2014). Grapheme awareness may thus be considered as an important early precondition which promotes the modification of visual processing of graphemes toward the analytic processing required for letter knowledge. Since, in turn, early letter knowledge has been shown to be one of the strongest predictors of later reading and writing success (Schatschneider et al., 2004; Leppänen et al., 2008), grapheme awareness may be considered an important first step in the process of learning to read and write (Lachmann, 2002; Lachmann and van Leeuwen, 2014; Lachmann et al., 2014).