Most children transition from presymbolic (e.g., gestures and vocalizations) to symbolic (e.g., words) communication during the first year of life. The transition into symbolic communication is at risk for many children with developmental delays including autism. When delays persist into preschool ages, children are frequently taught to communicate with some form of augmentative or alternative communication (AAC); however, little evidence exists linking specific child and environmental variables in AAC to communication outcomes. The researchers hope to identify variables that result in improved communication outcomes by prospectively studying 100 young children with developmental disabilities and 20 young children with autism spectrum disorders (ASD), all of whom will be learning to communicate with AAC. This research is likely to improve assessment and intervention practices for these children by identifying potential predictors of response to AAC interventions.