The study examined in this review analyzed whether a full two-year "Learning Experiences and Alternative Program for Preschoolers and Their Parents" ("LEAP") training and support model for teachers was superior in improving outcomes of preschool children with Autism Spectrum Disorder (ASD), as compared to a limited "LEAP" model in which no professional development support was provided. Fifty preschool classrooms from 16 districts and seven states across the United States were randomly assigned to either intervention or comparison conditions. Teachers in classrooms assigned to the intervention group received written "LEAP" materials, skill area presentations and demonstrations by "LEAP" trainers, onsite training and support, and maintenance checks. Comparison classroom teachers received written "LEAP" materials and videos, but no in-person training or ongoing support. In total, there were 177 children with ASD in the full "LEAP" training classrooms and 117 children with ASD in the comparison classrooms. The study found a positive impact after two years of the full "LEAP" training and support model on the average classroom-level measures of behavior, communication, intellectual outcomes, and social outcomes of preschool children. The average effect sizes for all four domains are statistically significant. The research described in this report meets What Works Clearinghouse (WWC) evidence standards without reservations. This study is a well-implemented randomized controlled trial. Three appendices include: (1) Study details; (2) Outcome measures for each domain; and (3) Study findings for each domain. A glossary of terms is provided. [The following study is the focus of this "Single Study Review": Strain, P. S., & Bovey II, E. H. (2011). Randomized, controlled trial of the LEAP model of early intervention for young children with autism spectrum disorders. "Topics in Early Childhood Special Education," 31(3), 133-154 (EJ942105).]