Comparing School Systems to Explain Enduring Birth Date Effects

Birth date effects refer to an association between children's academic performance and their age within the school year. Early differences show disadvantage for the youngest in the year group. Birth date effects of the same kind which show up at the senior levels of school have been reported in the UK. The phenomenon has been attributed to biology or individual psychology. Neither can explain why in some countries the youngest continue to be disadvantaged but in other countries they perform best. Population estimates from the IEA Third International Mathematics and Science Study and a comparison of school entry and selective promotion in the UK and New Zealand suggest that the explanation lies in the characteristics of the samples from which average scores are obtained and the extent to which they represent a full range of ability.