Student behavioral concerns are a top priority for school psychologists. This project took an ecological systems perspective by examining the contribution of students’ initial externalizing and internalizing behaviors and the quality of their classroom environments to their behavioral outcomes across one school year. Participants included 322 elementary students and their 32 teachers. Results suggested that externalizing and internalizing behaviors were stable over time. However, the correlation between fall and spring internalizing behavior was accentuated if students also had high externalizing behavior in the fall. Poor spring behavioral engagement was predicted by students’ fall internalizing (but not externalizing) behavior. Importantly, classrooms high in emotional support attenuated the stability of students’ internalizing behavior. In addition, students’ fall externalizing behavior appeared to be associated with reduced spring internalizing behavior in classrooms high in emotional support or classroom organization. Findings underscore the importance of considering both student‐ and classroom‐level factors when predicting elementary students’ behavioral outcomes.