* For a general school: l'école (pronounced "lay-kohl")
* For a specific school: le collège (pronounced "luh-koh-lehj") for middle school, le lycée (pronounced "luh-see-ay") for high school, l'université (pronounced "luh-ni-vair-si-tay") for university, etc.
Here are some examples:
* J'ai été à l'école aujourd'hui. (I went to school today.)
* Quel est ton collège ? (What is your middle school?)
* Je vais au lycée. (I'm going to high school.)
* Elle étudie à l'université. (She studies at the university.)
The specific word you use will depend on the type of school you are referring to.