Faced with the task of making data-based decisions about infant and toddler services (e.g., Response to Intervention: RTI), professionals need appropriate measure and tools to integrate progress monitoring and decision making procedures into their existing practices. Infant and Toddler IGDIs are play-based assessments that can be administered quickly (6 minutes) and frequently, and are sensitive to small changes in growth. The domains that they cover include language, motor skills, social engagement, and cognitive problem solving.