Preschool children with Autism Spectrum Disorder (ASD) may not always be recognized as such during their early years, but some of their behavioral problems may nonetheless prompt a referral for behavioral intervention. Whether such an intervention brings any benefit has not been well studied. We identified a subsample of 34 preschool children at risk for autism spectrum disorder from a large randomized controlled trial (N = 126) of the First Step to Success program. Children at risk of developing ASD demonstrated significant improvements on seven of 11 outcome measures and on a responder analyses based on symptom severity. Process and fidelity measures also suggested that First Step was both feasible and socially acceptable. Implications for early intervention for children at risk of developing ASD are discussed.