Background: Classrooms can create barriers to young autistic students' social and behavioral success at school. Better quality student-teacher relationships (STRs) have been associated with improved student social and behavioral outcomes. When teachers use more positive response strategies (e.g., praise), they create more opportunities for positive interactions with students, likely developing closer STRs.Method: The present study uses SEM to investigate a path by which teachers' use of positive response strategies is associated with closer STRs, which lead to improved social functioning and classroom engagement for N = 145 young autistic students (age 4-7 years). Factors contributing to teachers' reported frequency of using positive response strategies were also explored using multiple linear regression.Results: The model was a close fit to the data (chi 2 (18, N = 145) = 18.4, p = .43, TLI = 1.0, CFI = 1.0, RMSEA = .01). Teachers who reported using positive response strategies more frequently had significantly closer STRs, which were associated with lasting improvements in students' social functioning and engagement in the classroom. Positive response strategies that teachers reported using most frequently were praise, positive comments, and incentives. Teachers' perceived usefulness of positive response strategies and regular trainings in autism were significantly associated with frequency of positive response strategy use.Conclusions: Positive, supportive classrooms in which teachers utilized more positive response strategies and developed closer STRs were associated with young autistic students' academic engagement and social functioning. Regular autism trainings and perceived usefulness of positive response strategies emerged as significant factors for teachers' use of strategies.