Convention against Discrimination in Education

The UNESCO Convention against Discrimination in Education is a multilateral treaty adopted on 14 December 1960 in Paris and came into effect on 22 May 1962, which aims to combat discrimination in the field of education. The Convention also ensures the free choice of religious education and private school, and the right to use or teach their own languages for national minority groups. The Convention prohibits any reservation. As of December 2020, 106 states were members of the Convention.
It is the first international instrument which covers the right to education extensively and has a binding force in international law. It is recognized as a cornerstone of Education 2030 Agenda and represents a powerful tool to advance the Sustainable Development Goal (SDG4).
There is an additional Protocol Instituting a Conciliation and Good Offices Commission, which was adopted in 10 December 1962 and entered into force on 24 October 1968 in signatory States. As of October 2019, the Protocol has 37 members (including Vietnam; post-unification Vietnam has not expressed a position on whether it succeeds pre-unification South Vietnam as a member of the Protocol).
This Convention is also referred to in the "Preamble" of International Convention on the Elimination of All Forms of Racial Discrimination and UN International Convention on the Protection of the Rights of All Migrant Workers and Members of Their Families.
Contents.
Article 1 defines "discrimination" as any distinction, exclusion, limitation or preference on the basis of race, color, sex, language, religion, political or other opinion, origin national or social status, economic status or birth. 
However, the article indicates a number of situations which are not to be considered to constitute discrimination. This includes the creation or maintenance of separate educational systems or establishments for pupils of both sexes, when they have easy access to education:
Article 3 requires States to eliminate and prevent discrimination and Article 5 affirms respect for the freedom of parents in the choice of private schools, and for national minorities to have the right to engage in educational activities of their own and the employment or teaching of their own language. 
Article 9 prohibits any reservation to the Convention.
The treaty, in its entirety, may be viewed here.