Provisions in international law
Look to the Provisions of International Treaties
The arguments for constitutional amendment/legislation with the most leverage are those that seek the domestic enactment of ratified international conventions.
For example, any government that has ratified the Convention on the Rights of the Child (CRC) since its adoption in 1990 (all except the USA and Somaliland) is legally bound to comply with its provisions, including to ‘undertake all appropriate legislative measures necessary to implement the rights contained in the Convention.’ (CRC Article 4)
Even where a country has not ratified a treaty, it is still worthwhile attempting to push your government to enact legislation based on the provisions or general comments of the CRC or other relevant international treaties.
Consult the provisions of the global and regional treaties under international law. The merits of each are outlined there and there are useful indicators as to how the right can be framed.
The anti-discrimination provisions in most of the above treaties constitute the traditional groups of people by which societies have classified discriminatory practice. However, new groups are increasingly being excluded from education or are being more readily recognised as disadvantaged groups - it is important to ensure the groups that are at risk in your country are acknowledged as such.