The techniques of applied behavior analysis (ABA) are effective in altering the developmental trajectory of some very young children with autism. This research suggests that early, intensive treatment using the methods of ABA enables a significant number of children to enter the educational mainstream and achieve normal intellectual functioning. Both home-based and center- or school-based models have been used to deliver these services. Although discrete trial instruction is one of the most potent tools of early ABA teaching, a number of variations on this theme—the initial teaching of mands (requests), the use of an enriched environment with many items attractive to the child, and a focus on teaching the child to be highly skilled (fluent) in a behaviorall have the potential to be valuable teaching approaches.