A positive caregiver-teacher relationship has the potential to promote student progress. Yet, little is understood about factors contributing to effective caregiver-teacher alliance and team building on behalf of students with autism. Data from randomized controlled trials of a home-school collaborative planning and teacher coaching intervention called COMPASS were used to determine whether caregivers' perceptions of teacher alliance was associated with child goal attainment outcomes, and what caregiver and child factors were associated with alliance of the 75 caregivers, those who received COMPASS were more likely to report higher alliance compared to caregivers who did not receive COMPASS. Further, higher ratings of objective assessment of child goal attainment of social, communication, and learning skills were associated with higher alliance. For child variables, higher caregiver and teacher ratings of externalizing behavior were associated with lower ratings of alliance. Lastly, higher ratings of caregiving stress were associated with lower alliance. Autism severity, age, adaptive behavior, IQ and family income were not associated with alliance; however, caregiver stress was significantly associated. These findings demonstrate the association between alliance and child progress and how COMPASS improves alliance. Also, attention to caregivers of children with externalizing behaviors may be particularly warranted given the impact on caregiver-teacher alliance.