The effect of "temperament" in a school-like environment was evaluated for 30 children with mental retardation, 30 children with autism, and 30 typical children (all groups with a mean mental age of 23 to 24 months). Five-minute videotapes of each child attempting to complete a puzzle were viewed and scored by raters on the University of California (Los Angeles) Temperament Form. This instrument results in independent scores on the dimensions of activity, adaptability, approach/withdrawal, attention, distractibility, intensity, mood, and sensitivity. These dimensions are loaded into three factors: task orientation, personal social flexibility, and reactivity. Findings indicated that the children with autism differed significantly on dimensions of temperament in a negative direction from children with mental retardation or normally developing children. (DB)