Formal:
* Quel est le nom de votre école ? (This is the most formal way to ask.)
Informal:
* Comment s'appelle ton école ? (This is more casual and used with friends or people you know well.)
* C'est quoi le nom de ton école ? (This is very informal and could be considered slang.)
The best choice will depend on the context and your relationship with the person you are talking to.