I think: Az iskolában vagy? = Are you in the school? Iskolában vagy? = Are you in school?
"Are you inside the school" - is this an acceptable translation? Not sure if this sentence is about being in the school physically or generally attending school.
"Inside" is maybe a bit strong. The sentence can mean either and be translated as "Are you in/at school?" or "Are you in the school?"
"Inside" is usually translated with bent: "Bent vagy az iskolában?"