The cost of school uniforms should not be more than 5% of a family's monthly income, according to new uniform guidance from the Department of Education (DE).
The guidance does not set a limit on how much a uniform can cost.
But primary schools have been told not to ask pupils to wear any branded PE kit, and schools which are found not to have followed the DE guidance will be issued a published warning that includes their name.
In October, MLAs passed a law aimed at limiting the cost of school uniforms in Northern Ireland.
