Martine van der Pluijm

171 General discussion different contexts will be necessary, as customization to the specific conditions of the home environment of parents with different backgrounds. DBR can be a suitable method to find a feasible version of home support for both teachers and parents in several contexts by iterative testing in close collaboration with stakeholders. Second, researchers should investigate how existing instruments for assessing the home environment (e.g., the HOME) can be used and whether new instruments need to be developed so that teachers can better assess the HLE, enabling them to further adapt their support to the abilities and routines of families. Activities should be scheduled to the routines at home and designed to the abilities of parents. Our review (Chapter 2) shows the effectiveness of these types of flexible activities, such as talking about the past when walking to school or having playful dialogues during bathing (Boyce et al., 2010; Landry et al., 2008; Reese et al., 2010). A recent paper by Van Steensel et al. (2019) shows considerably higher effect sizes for these flexible activities targeting the language development of children, compared to scripted programs targeting a variety of aims. This brings us to our final recommendation. Future research could investigate whether applying the AHL design principles in the home environment of lower-educated families contributes to children’s language development. An important question is whether the additional delivery at home has an added value compared to the delivery of the program at schools only. Experimental research with involvement of lower-educated parents The studies in Chapters 3-5 took place in a small number of schools with highly diverse populations in Rotterdam. These studies focused on finding solutions prioritizing collaborative methods in school practices and establishing ecologically valid design principles that were tested by summative evaluations in case study research (e.g., McKenney & Reeves, 2012). We did not use an experimental design, comparing the intervention group to a (equivalent) control group. Therefore, we cannot conclude that the AHL approach is effective (Bryman, 2012). Future research is needed to investigate the generalizability of the AHL design principles and their effects on the oral language development of young children. We have four recommendations for researchers that want to contribute to the quality of future research, assuring that lower- educated parents are involved in ecologically valid research. First, we recommend specifically focusing on the specific group of very low educated parents. In our review study (Chapter 2), we only found a few studies that targeted this group of lower- educated parents. This finding is in line with the latest research showing a paucity of language interventions that target low-SES families (e.g., Greenwood et al., 2020; Heidlage et al., 2020). In addition, definitions of lower-education that are used in research (attained level of high school or less) differ from the international definition of the OECD that categorizes low education levels