The overall goal of this proposal is to develop and advance behavioral assessment methods (BAM) to measure spontaneous reach and grasp in infants and toddlers with and without hemiparetic cerebral palsy. Reach and grasp are critical to promoting healthy development and active engagement with the environment. This proposal focuses on the key period from 8 – 36 months of age when infants rapidly develop upper extremity skills, mobility, cognition, and language; and when hemiparesis-specific treatments, such as constraint-induced movement therapy, can be started. BAM will advance scientific knowledge about typical movements of the arms and hands as well as altered movements in children with hemiparetic cerebral palsy. This will yield a standardized, objective metric that quantifies the distance between impaired and typical development and will expand the precise measurement of treatment-induced recovery. This project includes prospective longitudinal data obtained from typically developing infants and toddlers and leverages video-sharing and support from StrokeNet’s Phase III randomized controlled trial of constraint-induced movement therapy. In AIM 1 we will develop the BAM Index using reach and grasp behaviors in 80 typically developing infants/toddlers and 240 infants/toddlers with perinatal arterial ischemic stroke and hemiparetic cerebral palsy. Videos will be coded for spontaneous reach and grasp frequency, duration, and exploratory behaviors with a common set of objects. Multiple statistical models will be employed to develop four standardized BAM Indices. In AIM 2 we will (a) evaluate the changes of four BAM Indices with 1040 longitudinal videos from the cohorts and (b) establish psychometric properties of the BAM Indices using: the Pediatric Stroke Outcome Measure (Neurological deficit and function); Gross Motor Function Measure-66 (Gross Motor), Bayley Scales of Infant and Toddler Development 4th edition (Fine Motor, Gross Motor, Language, and Cognition subscales), mini- and Assisting Hand Assessment (paretic hand); parent-reported outcome measures (Infant Motor Activity Log, MacArthur-Bates Communicative Developmental Inventories); and a combined clinical/parent outcome measure (Emerging Behaviors Scale). This project has the potential to advance pediatric rehabilitation research by affording a novel, reliable, precise, and sensitive measure of reach and grasp – applicable to hundreds of thousands of children with infant stroke and hemiparetic cerebral palsy. Furthermore, the novel use of data sharing and video coding are imperative for scientific reproducibility, reduction in cost, and will support the ability to improve health and physical function in infants and toddlers with cerebral palsy and other physical disabilities.