Is there that much of a difference from "What have you learned in school?"
Вчити (and its phonetic variant учити) can mean both, the exact meaning can be understood depending on the nouns you use with it:
- When it means ’to teach’, you use the person being taught in accusative case, and the subject being taught in dative case.
- When it means ‘to learn’, you use the subject being learnt in accusative case.
«Вчитися» also works in this sentence, but it requires a dative case for the subject being learnt: «Чому ви вчилися в школі?».