Purpose: The present study investigated school absence among 1,076 5-15 year-old children with neurodevelopmental conditions (intellectual disability and/or autism) approximately one year following the start of COVID-19 in the UK. Methods: Parents completed an online survey indicating whether their child was absent from school during May 2021 and the reason for each absence. Multi-variable regression models investigated child, family and school variables associated with absenteeism and types of absenteeism. Qualitative data were collected on barriers and facilitators of school attendance. Results: During May 2021, 32% of children presented with persistent absence (missing = 10% of school). School refusal and absence due to ill-health were the most frequent types of absence, accounting for 37% and 22% of days missed, respectively. COVID-19 related absence accounted for just 11% of days missed. Child anxiety was associated with overall absenteeism and with days missed because of school refusal. Parent pandemic anxiety and child conduct problems were not associated with school absenteeism. Hyperactivity was associated with lower levels of absenteeism and school refusal but higher levels of school exclusion. A positive parent-teacher relationship was associated with lower levels of absenteeism, school refusal and exclusion. Child unmet need in school was the most frequently reported barrier to attendance while COVID-19 was one of the least frequently reported barriers. Conclusion: COVID-19 had a limited impact on school attendance problems during this period. Findings highlighted the role of child mental health in different types of absence and the likely protective role of a positive parent-teacher relationship.