Developmental social pragmatic interventions for autism spectrum disorder (ASD) focus on development of strong interpersonal relationships by encouraging social communication during joint play routines. The goal of the current investigation was to conduct a randomized controlled 24-week pilot trial to examine the efficacy of a Developmental Reciprocity Treatment package (DRT-P), a developmentally-based intervention that includes both parent training and direct treatment with the child, compared to a delayed treatment group (DTG). Thirty-seven children aged 2-5 years with ASD and language delay were randomized. 83% of parents in DRT-P met fidelity of implementation criteria by 24 weeks. Controlling for fidelity, participants in DRT-P showed significantly greater improvement on the Social Responsiveness Scale Total Score (F = 5.00; p = 0.034) and the Clinical Global Impressions Improvement scale; however no significant group differences were observed on the Brief Observation of Social Communication Change, Vineland Adaptive Behavior Scales, or the MacArthur-Bates Communicative Development Inventories. Findings suggest DRT is a promising intervention for improving some aspects of social functioning in young children with ASD. Future research exploring how behavioral and developmental interventions can be optimally combined to target core social difficulties along with adaptive and functional communication skills is expected to be beneficial.