OBJECTIVE: Emotional availability (EA) describes caregiver-child emotional attunement and is critical to fostering adaptive development. Although early physical therapist interventions adopt a family-centered approach, the impact of interventions on families is often not quantified. This study compares EA in dyads receiving usual care-early intervention (UC-EI) versus sitting together and reaching to play (START-Play) in addition to UC-EI. METHODS: Data were drawn from 106 children with neuromotor delay who were 7 to 16 months old at baseline (mean = 10.5 months) and from their caregiver (91% were mothers). The Emotional Availability Scale, Fourth Edition, was scored from 5-minute videotaped interactions collected at baseline and at 3, 6, and 12 months after baseline. Piecewise multilevel modeling controlling for baseline age and motor delay estimated short- and long-term effects between treatment groups. Additionally, within-group change over time was analyzed to understand if groups differed in direction of EA trajectories. Analyses were run aggregated across all participants and stratified by baseline severity of motor delay or caregiver-reported education. RESULTS: When comparing EA between groups, there were significant positive short- and long-term effects of START-Play on adult EA (gs >
0.38), sensitivity (gs >
0.26), structuring (gs >
0.43), and nonintrusiveness (gs >
0.36). For dyads with mild or significant motor delay or whose parent reported less than a bachelor's degree at baseline, positive effects of START-Play were observed. CONCLUSION: Results support important clinical implications for the positive effect of START-Play on EA. Similar child-level treatment effects highlight that the key difference between START-Play and UC-EI may lie in the way intervention affects caregivers. START-Play may be more beneficial to dyads with higher versus lower risks to EA. IMPACT: Early physical therapist interventions can have a significant impact on parents, children, and the parent-child relationship. Measuring the effect of these interventions on the relationship is critical to optimizing the delivery of family-centered care.