Article 2 (1) of the International Covenant on Economic, Social and Cultural Rights (ICESCR) (1966) recognises that economic, social and cultural rights are not always immediately realisable. The full and immediate realisation of the right to education can be hampered by a lack of resources and can only be achieved over a period of time, particularly for countries with fewer resources.
The ICESCR therefore imposes the obligation to progressively realise certain aspects of the right to education (including free secondary, higher, and fundamental education). However, not all aspects of the right to education are subject to progressive realisation, for example, States must prohibit discrimination in and to education and ensure that primary education is free and compulsory for all.
For further information, see Right to Education Project’s page Understanding Education as a Human Right.
For further information on progressive realisation, see Committee on Economic, Social and Cultural Rights (2003) General Comment 3: The Nature of States Parties’ Obligations (Art. 2, Para. 1).