The adult illiteracy rate in 2000 was estimated at 44% (males 33%, females 55%). In 1997 there were 240,737 students and 5,476 students in 549 primary schools. In the same year there were 89,087 students and 2,071 teachers in secondary schools. The pupil-teacher ratio at the primary level was 48 to 1 in 1999. In the same year, 40% of primary-school-age children were enrolled in school, while 23% of those eligible attended secondary school. Many primary-school pupils are overage due to lack of previous access to education. Education is compulsory for children between the ages of 7 and 13. The educational system is comprised of five years of primary school, followed by six years of secondary school. There is a university in Asmara. In 1998, there were 198 teachers and 3,096 students in post-secondary education. As of 1999, public expenditure on education was estimated at 4.8% of GDP.