Preschoolers (n = 118) with autism spectrum disorder (ASD) participated in this prospective effectiveness study of an early intervention program. Treatment entailed parent training and therapist-implemented components, incorporating Pivotal Response Treatment and Positive Behaviour Support. Standardized ability and behavioural measures were gathered prior to and following the 1-year intervention. Analyses were conducted for three groups based on baseline IQ: Higher IQ (=70; n = 36), Moderately Low IQ (40-69; n = 40), and Very Low IQ (<40, n = 42). Observed gains in key language and cognitive outcomes were significant for all groups. Baseline cognitive scores significantly predicted 1-year outcomes. Results are encouraging for this relatively low-intensity community-based intervention program.