While the impact of authentic research experiences in STEM on student engagement and interest in science has been documented, less is known about the role of peer communities in fostering this interest and engagement. This research explores the idea that a strong peer community can catalyze deep learning and engagement in scientific research among high school students. The program engaged 20 high school students in a year-long community-based participatory research project in public health each year. The study used a mixed methods approach, combining data from focus group discussions, observations, and surveys to describe the program's impact on participants. Analysis across three years reveals that (a) the program was associated with a statistically significant shift in students' identity as researchers, with a medium growth effect size (Cohen's d) for the second and third years, which moderated by the end of the program, and (b) the peer community played a central role in the participants' engagement in the program, on their identity as researchers, and strengthened their interest in STEM. These findings convey the importance of designing STEM experiences that build strong peer communities around science practices and how such communities can have profound impacts on students' identities in STEM.