Does additional instruction in primary school improve secondary school outcomes? A re-evaluation of recent work in New Zealand.

Prior research finds that season of birth predicts a range of later outcomes. This thesis establishes that New Zealand babies born in winter are more likely to have a teenage mother, be Māori or Pacific, and have a low birthweight – characteristics associated with socioeconomic disadvantage. Yet, secondary school assessment results do not display prominent heterogeneity by month of birth. This stands in contrast with recent research that exploits variation in primary school instruction time that depends on season of birth, which ostensibly leads to large differences in secondary school achievement. This thesis investigates the apparent contradiction between these findings and observed assessment results. It concludes that the large effects reported in the earlier research result from sample selection bias. Correcting this bias confirms that season of birth (and hence primary school instruction time) has a relatively small impact on secondary school education outcomes in New Zealand.