The mandatory education age ranges between 5–7 to 16–18 years, contributing to an adult literacy rate of 99 percent. Just over 60,000 children are homeschooled as of 2016. In 2002, 43 percent of Canadians aged 25 to 64 possessed a post-secondary education; for those aged 25 to 34, the rate of post-secondary education reached 51 percent. The Programme for International Student Assessment indicates Canadian students perform well above the OECD average, particularly in mathematics, science, and reading, ranking the overall knowledge and skills of Canadian 15-year-olds as the sixth-best in the world. Canada is a well-performing OECD country in reading literacy, mathematics, and science with the average student scoring 523.7, compared with the OECD average of 493 in 2015.