It’s elementary: students benefit from pre-primary education. The OECD’s PISA 2009 results show that in practically all OECD countries 15-year-old students who had attended some pre-primary school outperformed students who had not. In fact, the difference between students who had attended for more than one year and those who had not attended at all averaged 54 score points in the PISA reading assessment – or more than one year of formal schooling (39 score points). While most students who had attended pre-primary education had come from advantaged backgrounds, the performance gap remains even when comparing students from similar backgrounds. After accounting for socio-economic background, students who had attended pre-primary school scored an average of 33 points higher than those who had not...