Research Design and Methods: This study will use a randomized controlled trial in which infants and their families are randomly assigned to the intervention group (START-Play in addition to usual services) or control group (usual early intervention services), stratified by severity of neuromotor disorder. There will be six measurement sessions during the 12-week intervention period, following by assessments during 1-, 3-, and 9-month follow-up visits. The study aims to determine the efficacy of the intervention on sitting and reaching (proximal outcomes) and motor-based problem solving skills (longer-term proximal outcome), which is hypothesized to serve as mediators to the more distal outcomes of global cognitive development and readiness to learn. The investigators will also explore fidelity of implementation to identify conditions that support fidelity and outcomes, as well as identify other moderating factors related to the child (severity of disorder, health, age, cognitive skill at entry), family (socioeconomic status, home environment), or services (fidelity of implementation, other services provided to child) to explore change over time.