Temperament is a construct that is relatively stable over time but varies between individuals. Research suggests that children with autism spectrum disorder have a ‘reactive’ temperament profile when compared to peers with or without disabilities. However, our understanding of how temperament varies within children with autism and how it relates to child symptoms and outcomes is limited. This study aimed to (a) explore the variation of individual temperament traits within a sample of school-aged children with autism to determine whether subgroups of children with similar trait profiles emerge and (b) examine whether temperament influences the relationship between autism symptoms and adaptive functioning outcomes. Results revealed that children with autism can be classified empirically into two distinct profiles – ‘Even’ and ‘Reactive’ temperaments. Correlational and hierarchical regression analyses indicated that both temperament profiles and baseline symptom severity predicted adaptive functioning outcomes 1 year later. There was a significant interaction between temperament and symptom severity, suggesting temperament can influence the impact of increasing symptom severity on adaptive functioning skills in children with autism. Study findings highlight the importance of considering temperament in understanding the individual differences that influence the development of daily functioning and developmental outcomes in children with autism. Lay Abstract Temperament is often thought of as behavioural traits that are relatively stable over time but can vary between individuals. Children diagnosed with autism spectrum disorder are often characterized as having ‘reactive’ and ‘negative’ temperaments when compared to same-aged peers with or without disabilities, which can negatively impact the development of adaptive functioning skills but little is known about variations of temperament between individual children diagnosed with autism spectrum disorder. This study aimed to (a) explore the variation of individual temperament traits within a sample of school-aged children with autism spectrum disorder to determine whether subgroups with similar trait profiles emerge and (b) examine whether temperament influences the relationship between autism symptoms and adaptive functioning outcomes. Results from our dataset suggest that children diagnosed with autism spectrum disorder fit under two profiles: ‘even’ and ‘reactive’. Furthermore, our analysis shows that temperament can influence the impact of increasing symptom severity on adaptive functioning skills in children with autism spectrum disorder. Study findings highlight the importance of considering temperament when trying to understand the individual differences that influence the development of functioning and developmental outcomes in children with autism spectrum disorder.