Lebanon's illiteracy rate is relatively low for the Middle East. For the year 2000, adult illiteracy rates were estimated at 13.9% (males, 7.7%; females, 19.6%). Free primary education was introduced in 1960, but about two-thirds of all students attend private schools. In 1997 there were 382,309 pupils in 2,160 primary schools. In the same year, there were 347,850 secondary school students. The pupil-teacher ratio at the primary level was 19 to 1 in 1999. In the same year, 71% of primary-school-age children were enrolled in school, while 70% of those eligible attended secondary school. In 1996, the total enrollment for all higher-level institutions was 81,588 students with 10,444 instructors. Leading universities include the American University in Beirut; St. Joseph University; the Lebanese (State) University; the University of the Holy Spirit; and the Arab University of Beirut. As of 1999, public expenditure on education was estimated at 2.1% of GDP.