Science talk is central to learning in the classroom but despite a variety of interventions, lack of participation in discussion is a persistent obstacle to learner engagement (Clarke, 2015; Mercer, 1996; Mercer et al., 1999; Webb, 1989). Classroom programs may aid student participation but have not been sufficient to overcome students' unwillingness to participate (Hogan, 1999; Olitsky, 2007; Wiltse, 2006). In this design-based research intervention study, guidance in the form of instruction, training, and scaffolds were iteratively designed to facilitate productive scientific discourse between sixth-grade science students and their parents. The main sources of data were recordings of 21 homework assignments during which parents prompted students to evaluate models based on evidence. The features of the intervention were examined using qualitative and quantitative methods. Suggested prompts for parents and a scaffold for model-evidence coordination (based on the work of Rinehart et al., 2014) were responsible for most students making connections between the evidence and one or more of the models. Parents used the suggested prompts and many of them took an active approach by elaborating on the suggested prompts. These parent-initiated questions outside of the suggested questions and materials resulted in more students giving high-quality responses that explained why a model was either a good fit or one that should be ruled out. The results demonstrate that with guidance, parents helped students engage in scientific discourse. The implications of these interactions on student learning are discussed. The findings may be used for future family engagement programs and interventions to build student understanding through talk. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]