Secondary education or post-primary education covers two phases on the International Standard Classification of Education scale. Level 2 or lower secondary education (less commonly junior secondary education) is considered the second and final phase of basic education, and level 3 upper secondary education or senior secondary education is the stage before tertiary education. Every country aims to provide basic education, but the systems and terminology remain unique to them. Secondary education typically takes place after six years of primary education and is followed by higher education, vocational education or employment. In most countries secondary education is compulsory, at least until the age of 16. Children typically enter the lower secondary phase around age 12. Compulsory education sometimes extends to age 19.
Since 1989, education has been seen as a basic human right for a child; Article 28, of the Convention on the Rights of the Child states that primary education should be free and compulsory while different forms of secondary education, including general and vocational education, should be available and accessible to every child. The terminology has proved difficult, and there was no universal definition before ISCED divided the period between primary education and university into junior secondary education and upper secondary education.
In classical and medieval times, secondary education was provided by the church for the sons of nobility and to boys preparing for universities and the priesthood. As trade required navigational and scientific skills, the church reluctantly expanded the curriculum and widened the intake. With the Reformation the state wrestled the control of learning from the church, and with Comenius and John Locke education changed from being repetition of Latin text to building up knowledge in the child. Education was for the few. Up to the middle of the 19th century, secondary schools were organised to satisfy the needs of different social classes with the labouring classes getting 4 years, the merchant class 5 years, and the elite getting 7 years. The rights to a secondary education were codified after 1945, and some countries are moving to mandatory and free secondary education for all youth under 19.