In 1985, behaviour analysts at the Princeton Child Developmental Institute published the first study showing that ABA programming was comprehensive i.e. using multiple behaviour analytic methods to address multiple skill domains, intensive provided in a 1:1 adult:ratio ratio initially for 27.5 hours per week, 11 months per year, and of a duration of two years produced substantial improvement in young children with an autistic spectrum disorder (fenske, Zalenski, Krantz, and McClannahan, 1985). In a quasi-experimental study, those investigators found that 6 of 9 children who entered centre-based ABA programming prior to the age of five had positive treatment outsomes after two years, defined as living at home and enrolled full-time in public schools woth no special support.

In 1987 Dr Lovaas of the University of Los Angeles California (UCLA) conducted the first experimental study of the effects of comprehensive, intensive, long-duration ABA programming for young children with ASD. This study documented substantially improved functioning in a sizeable proportion of the 19 children in the experimental group who received home-based, one-to-one ABA treatment for 40 hours per week for at least two years, having started the programme prior to the age of four. In contrast, few gains were made by the vast majority of of the 40 children in the two control groups who received either 10 hours of ABA treatment per week or typically available community services. A followup study found that the "best outcome" children from the Lovaas study (1987) maintained treatment gains into adolescence with no intervening special services (McEachin, Smith and Lovaas, 1993).

Empirical evidence corroborating the Lovaas findings is available. In a single group pre-test/post-test evaluation, Weiss (1999) found that 9 of 20 children with a diagnosis of ASD who received home-based ABA treatment for 40 hours per week for two years had post-treatment scores on the Childhood Autism Rating Scale that were clearly in the non-autistic range. Additionally, outcomes similar to those achieved by the "best outcome" children in the Lovaas (1987) study have been documented in systematic case studies in which children received home-based ABA treatment for 30-40 hours per week for at least two years, and independent evaluators used objective measurement instruments to track children's progress (Green, Brennan, and Fein, 2002; Perry, Cohen, and De Carlo, 1995).

Two recent research projects further support the efficacy of early intensive bhevaioural intervention for children with ASD. In 1999 Dr Glen Sallows of the Wisconsin Early Autism Project released a paper on Replicating Lovaas' Treatment and Findings:Preliminary Results (www.wiautism.com) and in 2005 Howard et al published a research paper on A comparison of intensive behaviour analytic and eclectic treatments for young children with autism (www.sciencedirect.com)