know, the quicker they can learn new ones (Nagy & Scott, 2002).
We believe that both variants of the program have the potential to enhance children’s vocabulary to an even larger extent. Treatment fidelity data demonstrate that implementation of the interventions was adequate, but that in both conditions parents’ involvement varied and decreased over the school year. Implementation can be improved by more intensive guidance of parents, or increasing the need for parents to visit the meeting. TL parents visited more parent meetings, suggesting that the digital component resulted in a need for instruction. In addition to implementation, other challenges might have impeded the success of the programs. There were many steps to take in order to establish vocabulary effects; first researchers trained teachers, then teachers trained parents and finally parents conducted the program at home to foster their child’s vocabulary. For such a stepwise process with many different people involved to be successful, a precise routine is required. The four parent meetings might have been too limited to implement this process optimally. Moreover, with regard to the TL condition, unforeseen technical issues were faced, such as insufficient wifi-connections, teachers and parents with limited digital experience, and the technology-enhanced storytelling activity giving errors. AL and TL were effective for children’s receptive vocabulary development despite these practical challenges, but there is still room for improvement in the implementation of the program.
With respect to the second research question, no differential effects of AL and TL were found. AL and TL did not interact with family contextual factors or the child’s executive or social functioning. This is consistent with the results of the systematic review of Burger (2010) and the meta-analysis of Van Steensel and colleagues (2011), which both demonstrated that children benefit equally from early interventions, regardless of their family background or their own capacities. Our study contributes to these findings. Our alternative AL and TL approaches fit the needs of different kind of families (higher and lower educated, L1 and L2) and children (with lesser and greater executive and social functioning). However, they do not have the potential to compensate for differences between children related to the family context or the child’s executive or social functioning. Although there were no differential effects of the intervention by family context and the child’s functioning, results do emphasize the large impact these factors have on children’s vocabulary. Girls, children with higher executive functioning and social functioning skills, and children from higher educated mothers and growing up in L1 families had larger vocabularies. Girls and L2 children showed
larger vocabulary growth, compared to boys and L1 peers. This indicates that L2 children have smaller initial vocabularies, but are able to catch up when entering preschool. These results confirm the large vocabulary differences that exist between children at preschool (Fenson et al., 1994; Teepe et al., 2016; Van Druten-Frietman et al., 2015).
For policy, our results indicate that it is of importance to invest in the home environment to increase the vocabulary of young children. In addition to providing education within the preschool, the center-based approach, policy makers should also consider investing in parents and the home environment in a combined approach. Even though the effects are small they are still meaningful. Because both variants of the family literacy program turned out to be effective, policy makers should carefully weigh the strengths and limitations of AL and TL mentioned above. Depending on their opinion of support, they could provide the program to all children, as the program proved to be effective for all children, regardless of background. However, if the goal of the government is to help children with smaller vocabularies offering the program to just those children with a smaller vocabulary could also be considered. In spite of this study’s strengths, some important limitations must be noted. First, because of policy constraints, we were not able to randomly assign preschools to conditions. This might have resulted in selection effects, even though no significant differences between conditions were found at pre-test. Second, we are aware that results largely depend on the words selected for the curriculum-based tasks. Per theme, we selected 16 nouns that, in our opinion, together reflected the content of that specific theme and were matched in difficulty based on word frequency lists. However, children might very well also have learned other words that were not present in our tests. Related to this, many children already showed high scores at pre-test, which would have reduced the potential of the test to show vocabulary growth. Third, the sample suffered from random attrition resulting in reduced statistical power.
Our findings point towards research opportunities for the future. The current study examined effects of AL and TL at child level. To gain better insight in the working mechanism of family literacy programs, future studies need to adopt measures demonstrating effects of family literacy programs on skills and perceptions of parents. Changes in the interaction behavior of parents and children need to be examined in a similar manner, for example by means of video-observations. Secondly, taking into account the later development of children’s productive vocabulary, a productive retention test would demonstrate whether the interventions used here have an (delayed) effect