Supporting student interest in science is critical for broadening participation in the field because interest, even more than achievement, is associated with pursuing future science education and careers. In this study, we explore the conjecture that equitable classroom cultures can support interest in science. Specifically, we examine the idea that science classroom cultures that equitably reflect collective enterprise (where students engage collaboratively in scientific sensemaking) and care (where students believe that they are valued and respected members of the classroom community) support students, particularly those from historically marginalized populations, to develop interest in science. The study is part of a field test of a new middle school science curriculum called OpenSciEd. Data consist of survey responses from 847 students across 34 teachers located in nine states. Our analysis employed mixed-effects models to accommodate the nested structure of the data. We found that classrooms vary substantially in the degree to which they reflect collective enterprise and care, indicating that classroom culture is a perceptible and consequential feature of the shared classroom environment. Student background did not predict reports of collective enterprise or care, providing evidence that classrooms in our sample were equitable along these dimensions. Critically, collective enterprise and care are both strongly associated with student-reported interest in science. These findings underscore the importance of attending to classroom culture and the relational aspects of science learning as we seek to expand interest in science, particularly for students from historically marginalized populations.