Science instruction reform efforts call for increased opportunities for students to engage with science content and practices. School-based citizen science (CS), when implemented well, addresses this call and provides a meaningful context for student learning. Despite CS projects' increasing role in formal science instruction, research on the potential for learning and conditions that support learning in CS contexts is thin. Using case study findings, this report discusses factors that affect teachers' decisions to integrate CS, as well as implications for supporting the uptake of effective school-based CS.