If you as a Christian are not allowed to pray in school, I assume you live in one of those strict Muslim countries where they kill people for not believing the right thing. And if you live in such a country, I’d like to know how you got access to this website in order to post your question?
In most other places, to the best of my knowledge, it is tolerated if Christians bow their heads in private and say a prayer. As I understand it, Muslims must pray several times a day with other Muslims in a very elaborate manner to correctly practice their religion. I further understand that only Muslims pray in these prayer rooms.
I have also read about Christians meeting in small rooms for Bible study. If you asked your school, perhaps they would provide a prayer room for you and your fellow-Christian students. As I am sure we all know, it is one thing for like-minded people to meet for rituals in a small room; it is another to make the entire diversely-minded public in the classroom to pray along with us to our own God/god.