Education in Greece is compulsory between ages 6-15 and includes primary school (ages 6-12) and lower secondary school (ages 12-15). Optional pre-school education is available starting at age 2.5. Post-compulsory secondary education consists of unified upper secondary schools lasting 3 years or technical/vocational schools lasting 2-3 years. Public higher education includes universities and technology institutes, which students enter after national exams in the second or third year of upper secondary school or by lottery at age 22 for open university.