Using data drawn from the National School Effectiveness Study, this paper reveals that by Grade 4 35% of South African learners are overage. The study confirms what every other testing programme tells us about the poor state of learning which characterizes the system: the seeds of low pass rates at Grade 12 level, and of low participation and throughput rates in further and higher education, are sown in the first three years of schooling. What the present study adds to this picture is that overage children perform less well than their appropriately aged peers, gain less learning from one year to the next, generally come from poorer homes than their appropriately aged peers, and are predominantly male. This is a major problem in the system, and giving explicit attention to it must constitute a significant component of any strategy to address the very poor learning outcomes of the school system, the slow progress of learners through the grades, and the high rate of dropouts in the last three years of the secondary school. (Contains 7 tables, 9 footnotes, and 6 figures.)