This paper charted the cognitive and behavioural profiles from toddlerhood to middle childhood in 48 children diagnosed with ASD at 24 months. The Mullen Scales of Early Learning (MSEL) was administered at 24- and 48-months and the Wechsler Abbreviated Scale of Intelligence (WASI) at school age. Autism severity was derived using The Autism Diagnostic Observation Schedule (ADOS). Results: Developmental Disability/Intellectual Disability (DD/ID; Developmental Quotient <70) reduced from 64% at 24-months to 8% at outcome. Seventy-three percent of children continued to meet ADOS cut-off at school age. Conclusion: Diagnoses at 24-months, appear to be reliable and stable. Further research is needed to investigate whether early identification, which provides more opportunity to access early intervention, may in turn facilitate cognitive development over time.