Background: There is limited research examining the efficacy of early physical therapy on infants with neuromotor dysfunction. In addition, most early motor interventions have not been directly linked to learning, despite the clear association between motor activity and cognition during infancy. Objective: The aim of this project is to evaluate the efficacy of Sitting Together And Reaching To Play (START-Play), an intervention designed to target sitting, reaching, and motor-based problem solving to advance global development in infants with motor delays or neuromotor dysfunction. Design: This study is a longitudinal multisite randomized controlled trial. Infants in the START-Play group are compared to infants receiving usual care in early intervention (EI). Setting: The research takes place in homes in Pennsylvania, Delaware, Washington, and Virginia. Participants: There will be 140 infants with neuromotor dysfunction participating, beginning between 7 to 16 months of age. Infants will have motor delays and emerging sitting skill. Intervention: START-Play provides individualized twice-weekly home intervention for 12 weeks with families to enhance cognition through sitting, reaching, and problem-solving activities for infants. Ten interventionists provide the intervention, with each child assigned 1 therapist. Measurements: The primary outcome measure is the Bayley III Scales of Infant Development. Secondary measures include change in the Early Problem Solving Indicator, change in the Gross Motor Function Measure, and change in the type and duration of toy contacts during reaching. Additional measures include sitting posture control and parent-child interaction. Limitations: Limitations include variability in usual EI care and the lack of blinding for interventionists and families. Conclusions: This study describes usual care in EI across 4 US regions and compares outcomes of the START-Play intervention to usual care.