Background: Student academic behavioral engagement (BE) contributes to learning and school success. Student-teacher relationships (STRs) may promote BE, although previous findings regarding how these constructs are associated over time are mixed. For young autistic students who face barriers to early school success, a high-quality STR may serve as a key protective factor to promote classroom engagement. Methods: The present study investigated connections between teacher-rated STR quality and student BE over two school years for 146 young autistic children (grade PK-2) using cross-lagged structural equation modeling. A full model with cross-lagged paths from BE to STR quality and from STR quality to BE was first examined. Potential confounding variables (i.e., externalizing behaviors, cognitive skills, and language skills) were included. The model was then trimmed by removing all non-significant paths. It was hypothesized that the final model would highlight the unidirectional influence of STR quality on BE. Results: Results supported the unidirectional influence of STR quality on BE across one school year. STR quality at the beginning of the first school year predicted behavioral engagement at the end of the year ([beta]=0.26, p<0.01) BE outcomes persisted into the following school year ([beta]=0.45, p<0.001). Conclusions: Findings suggest that STR quality significantly contributes to engagement for young autistic students, potentially serving as a critical protective factor for classroom success. This highlights the importance of developing quality STRs with high levels of closeness and low levels of conflict for students on the spectrum in early schooling.