For example, PISA shows that, in nearly all countries and economies, students who had attended pre-primary school tend to perform better at the age of 15 than students who had not attended, even after accounting for students' socio-economic status. Fifteen-year-old students in 2012 were more likely than 15-year-olds in 2003 to have attended at least one year of pre-primary education. But the rate of increase in pre-primary enrolment is higher among advantaged students than disadvantaged students, which means that the socio-economic gap between students who had attended pre-primary education and those who had not has widened over time.