Science education researchers increasingly focus on the use of controversial science topics in the classroom to prepare students to make personal and societal decisions about these issues. However, researchers infrequently investigate the diverse ways in which students learn about controversial science topics outside the classroom, and how these interact with school learning. Therefore, this study uses qualitative, ethnographic research methods to investigate how 20 high school students attending a New York City public school learn about a particular controversial science topic—HIV/AIDS—in different contexts, as well as how different sources of learning interact. In addition to finding that learning about HIV/AIDS happens across seven contexts of students' lives in diverse ways, including and beyond school settings, this study finds that students integrate learning that happens in these different contexts to shape their understandings and perspectives on HIV/AIDS issues. These findings are used to discuss the place of school learning within students' thinking about HIV/AIDS, highlighting ways in which students both value and discount their school learning in relation to other sources of learning. On the basis of our analysis, we make suggestions for bringing different sources of learning into the classroom to facilitate critical analysis of controversial science topics. © 2010 Wiley Periodicals, Inc. Sci Ed95: 87–120, 2011