I require my top band students to be in lessons. However, allow fundraiser money to "forgive" portions of their band fees and I also have a great booster club who helps to provide scholarships for students who need a financial boost.

For a parent who wants to go legal with this-there are other ensembles they can be a part of if they refuse to take lessons. I have yet to come across that because we provide so many ways to fund lessons. If your admin supports your policy you likely have a leg up. If a parent can afford to sue you over that they can afford to pay for lessons-easily.

I also have never seen a student not in lessons get better as students in lessons typically do get better. I make region band auditions a major requirement to varsity band membership and we have scored pass offs several times in the fall semester. (HS band here) If they fall below a score threshold they can lose their position in the varsity band. Kids in not in lessons...likely to not be successful.

You can win this battle.