Science education should help children acquire sophisticated understandings about science, how it is done, and how they can be scientists. Consequently, there is a need to explore how minoritized children's linguistic and cultural resources can be employed in the science classroom. This study examined how perceptions of science teaching and learning in bilingual contexts shift from a single tradition to more expansive understandings. Following cultural historical activity theory (CHAT), mediators and turning points were explored to provide evidence for expansive learning. This analysis focused on data from 25 children and four teacher candidates participating in a Spanish bilingual after-school program. To answer the research questions, expansive and non-expansive actions (i.e., speech segments and multimedia products generated in the 10 after-school sessions) were analyzed mostly qualitatively, and supported with descriptive quantitative patterns. Through the analysis, specific mediators and contextual characteristics were identified as turning points for expansive learning. The in-depth analysis of the four after-school sessions including both discourse and multimedia data, revealed the existence of a turning point in one session during which there was a discussion using a video and a multimodal embodied experience with clay. This session included turn and talks, and closed with a whole-group debriefing. Additionally, the study found that the multimedia artifacts (actions around photographs and videos) were more conducive to expansiveness than those with discursive data only. The study concludes that culturally relevant artifacts, combined with instructional moves that accept bilingual children's expansive ways of understanding science, stimulate expansive learning. This study provides ways to explore how bilingual children's out-of-school knowledges can merge with science knowledge in schools, and helps illuminate the role of multiple activity systems in the teaching and learning process. Furthermore, the study highlights the importance of having pre-service teachers explore the potential of children's out-of-school knowledges in spaces such as after-school programs where curricular and instructional restrictions are lessened, and that thus favor more expansive forms of teaching and learning.