not using the hijab is considered to be neglecting a Quranic instruction, which is tantamount to disobeying God. The penalty for this disobedience would then be for God to decide. And, if you ask some Muslims what that penalty would be, they will most likely say hell!This is why the question remains contentious in the Muslim world.. Meanwhile, the school is seen as a secular sphere where any form of religiosity must be suppressed.
Historically, schools were introduced by Christian missionaries as part of a project to spread the religion from 1843. This meant that missionaries embedded religious practices in schools. In primary and secondary schools, pupils pray in their assemblies and sing hymns. That's why I believe that the argument about Nigerian schools being secular is not only misleading - it's baseless.