It’s basically saying that the person’s mom often tells the person to try harder in school and practice playing their instruments. “Getting on” someone means that they are bugging someone about doing something. It’s usually seen as nagging or annoying someone. But sometimes it just means someone wants you to do what you’re supposed to, like a sports coach or teacher at school. Example: I haven’t cleaned my room in weeks! My mom has started to get on me about it. She has been driving me crazy. I hope this helps!