Late school entry prevails in many developing countries, and a brief international comparison suggests it has a general negative impact on school retention rates. Yet this widespread phenomenon has received little attention. This essay investigates late school entry in one of the larger countries in sub-Saharan Africa, Mozambique, for which data were available that allowed a detailed investigation. It demonstrates that in Mozambique pupils who enter school late have substantially higher drop-out rates than young entrants and may have, in addition, higher repetition rates. The essay also shows that many pupils in first grade are probably older than reported by the schools. The data necessary for the calculations include school attendance statistics from the Ministry of Education and from the 1997 Population Census.