When I'm at school I miss 2 prayers. What should I do?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

As long as your school is not on a distance that legitimizes it for you to shorten the prayers, you have to perform the prayers on their fixed times.  The distance that gives one the right to shorten the prayers is 83 Km or more.

However, if you cannot perform prayers in their early times at least you have to perform them later before the prescribed time ends.

However, if you are so compelled that you cannot get permission of a few minutes to perform prayers, you are allowed to combine the two prayers, i.e. Zuhr with Asr or Maghrib with Isha.  But it is not allowed to make it as a habit.

Allah knows best.