New school transitions can be challenging for students on the autism spectrum. No published, evidence-based interventions exist to support families and teachers of students transitioning to elementary and secondary school during this critical period. Using Community Partnered Participatory Research, we developed Building Better Bridges (BBB), a caregiver coaching intervention that includes training on effective school communication, educational rights, advocacy, and child preparation strategies. We compared BBB (n = 83) to a module/resources-only comparison (n = 87) in a four-site randomized controlled trial in racially and ethnically diverse, under-resourced communities. In our intent-to-treat analysis, caregivers and teachers in BBB rated students' transitions to the new classroom as more positive, relative to the comparison group. Results suggest this low-cost intervention can improve the transition process for families and students at high risk of poor transitions.