We trained parents to conduct functional analyses and functional communication treatment for 28 young children with developmental disabilities who displayed aberrant behavior. Of this sample, 22 parents conducted treatment for at least 3 months and 11 for 1 year. We conducted single-case analyses of the results of assessment and treatment. The functional analysis identified social functions (positive and negative reinforcement) for 86% (24 of 28) of the children. Treatment resulted in a pre/post decrease in aberrant behavior averaging 87% across the range of children, with the greatest decrease occurring at 3 months. Appropriate social responding increased, on average, by 69% across the range of children. Decreases in aberrant behavior were demonstrated in all children, and all except one child displayed increased social behavior during treatment. On a measure of parent-rated treatment acceptability, ranging from 1 (not at all acceptable) to 7 (very acceptable), the average overall acceptability was 6.35.