The association of maternal nutrition and children’s pre-primary experience with over-age attendance in secondary school: evidence from lowland Nepal

•Over-age attendance is increasing but remains under-studied in South Asia.•Children fall behind by entering pre-primary or primary late, and by repeating a grade during/after primary school.•Rural location, thin and uneducated mothers predicted late pre-primary entry.•Educational research and interventions need to focus on the earlier time-point of pre-primary.•Improving maternal nutrition and education may ensure timely progression of children in school.