Children typically learn by attending to other people. Autism traits may impact access to social stimuli fundamental to early learning, increasing children’s likelihood of a learning disability. Recent reports have highlighted that Autistic children from minority backgrounds have a higher likelihood of co-occurring intellectual disability. This study aimed to firstly confirm that early autism traits are concurrently and prospectively associated with lower developmental quotients, and secondly to examine the developmental and functional gains in Culturally and Linguistically Diverse (CALD) and non-CALD Autistic children following one year of Group-based Early Start Denver Model (G-ESDM). Secondary data on 114 non-CALD and 91 CALD Autistic preschoolers receiving the G-ESDM was utilised to address the study aims. Children were administered the Autism Diagnostic Observation Schedule (ADOS) at entry into the service. The Mullen Scales of Early Learning and the Vineland Adaptive Behaviour Scales-II were administered at both entry (Time 1) and 12 months later (Time 2). While no concurrent associations were found between autism traits and Developmental Quotient (DQ), significant associations were found prospectively with ADOS scores at Time 1 and DQ at Time 2, holding for both groups after controlling for DQ at Time 1. Autistic children made significant gains in cognition and functional behaviour following one year of early therapy, with no differences between the two groups. The results indicate that young Autistic children make significant gains in early development and add to the sparse research on the developmental and functional outcomes of Autistic children from CALD communities.