In this study, we explored how science teacher candidates construct ideas about science teaching and learning in the context of partnerships with urban community-based organizations. We used a case study design focusing on a group of 10 preservice teachers' participation in educational programming that focused on environmental racism and connected science to larger social issues in an economically dispossessed Mexican community in Chicago. Using theoretical lenses of humanistic science education, justice-centered science pedagogy, and structure-agency dialectic, we studied how preservice high school science teachers made sense of equity and social justice issues facing marginalized communities and how they thought about the goals and nature of science education, along with their role as science teachers, as they participated in a Toxic Tour provided by the Little Village Environmental Justice Organization. By emphasizing both environmental challenges and the community assets in Little Village, the Toxic Tour provided an opportunity for science teacher candidates to develop a complex understanding of this particular community and critically reflect on their own communities. The teacher candidates identified both structures that are enabling or disabling for community members "and" people's individual and collective agency acting upon these structures. They also recognized communities as places of authentic science learning.