Children on the autism spectrum miss more school than their peers, but limited work has explored why this may be. This study aimed to document the frequency at which children on the autism spectrum miss half and full days of school and the reasons for these absences. Parents of 106 school-aged children on the autism spectrum completed online questionnaires on rates of school non-attendance, family factors, child anxiety, and parental mental health. On average across a four week period, children missed 6 full days of school. The most common reason for full-day absences was school refusal and for half-day absences was medical/therapy appointments. Parental employment status, increased child age, child anxiety, and differing aspects of parental mental health were identified as correlates of specific subtypes of school non-attendance.