As the prevalence of autism spectrum disorder has expanded over the last two decades, comprehensive treatment models have been developed to promote the learning and development of young children with autism and welfare of their families. Comprehensive treatment models exist along a continuum. At one end of the continuum are highly structured modes of teaching, which target core and associated features of autism, through such instructional components as minimizing classroom distractions. Project TEACCH represents such a comprehensive model. At the other end of the continuum are naturalistic teaching approaches, which target those features by providing treatment in contexts similar to prototypical early childhood classrooms. The LEAP model exemplifies a naturalistic comprehensive intervention approach. The purpose of this study funded by the Institute of Educaton Sciences was to examine the immediate and long term effects of these two comprehensive treatment models, as compared with each other and a "business as usual" (i.e., typical service) model.