Telehealth coaching in Project <scp>ImPACT</scp> indirectly affects children's expressive language ability through parent intervention strategy use and child intentional communication: An <scp>RCT</scp>

Parent-mediated, naturalistic developmental behavioral interventions (NDBIs) are a promising approach for supporting social communication development in young autistic children. This study examined the effect of telehealth delivery of a parent-mediated NDBI, Project ImPACT, on children's expressive language ability using a randomized control trial with intent-to-treat analysis. Sixty-four young autistic children and their primary caregiver were matched on age and developmental quotient and randomly assigned to receive 6 months of therapist-assisted Project ImPACT (i.e., telehealth coaching), self-directed Project ImPACT, or an active control. Parent-child interactions were recorded at intake and immediately post-treatment, and the children's expressive language skills were assessed at intake and a 9-month follow-up using standardized measures. Although there was no total effect of treatment group assignment on child outcomes, a serial mediation analysis revealed that therapist-assisted ImPACT had an indirect effect on children's expressive language ability at follow-up through their parents' use of the intervention strategies and their intentional communication immediately post-treatment. Findings support Project ImPACT's program theory and highlight the importance of coaching in achieving positive outcomes when delivered via telehealth.