Responsive Teaching: Relationship-Based Developmental Intervention (RT) is an evidence-based developmental curriculum designed for early intervention professionals who work with parents and other caregivers to support and enhance their children's development in the natural environment. RT was derived from research investigating how parents' interactive relationships are associated with the development and well-being of children with developmental disabilities and risks. It includes detailed instructional strategies, procedures, and session plans for addressing children's needs across three developmental domains: cognition, communication, and social emotional functioning. RT was first published under the title Autism and Developmental Delays in Young Children: The Responsive Teaching Curriculum for Parents and Professionals (Mahoney and MacDonald, 2007). This revision includes several new features.