Peer cultures of effort and achievement influence early adolescents' academic adjustment. A randomized controlled trials design was used to test the extent to which aspects of peer cultures of effort and achievement were enhanced following teachers' participation in the Supporting Early Adolescents' Learning and Social Success (SEALS) intervention. Observational and survey data from teachers (N = 188) and survey data from 6th-graders (N = 2,453) in 36 rural schools across the United States were analyzed. Results indicated that in SEALS versus matched control schools, social prominence was more favorably associated with effort and school valuing, and peer group injunctive norms were more supportive of effort and achievement. Findings indicate that aspects of peer cultures respond to the school context and provide evidence of the efficacy of the SEALS model.