We argue that Latino/a students are more likely to major in science, technology, engineering, and math (STEM) in college if they were educated in high schools where they studied with satisfied teachers who worked in collaborative professional communities. Quantitative results demonstrate that collaborative professional communities in high school are important for Latino/a students' choice of major in college. Results from qualitative interviews clarify how Latino/a students' perceptions of precollege educational environments shape their decisions to major in STEM.