Had precisely that problem when my son was in middle school. The school learned that he was shooting regularly and wanted to know where he got a gun and how - he said, "Ask my dad, he's an instructor." That wasn't good enough for them - they called my at work and told me that matter involving my son needed to be discussed ASAP. Drove straight to the school, imagining all kinds of things -first question put to me was, "Under what authority to you allow your son to handle a gun?"
I was caught off guard by the question; therefore took my time formulating an answer: First it is none of your business - it does not occur during school hours. Second, he is my son and my responsibility, not yours. When he (the Principal) attempted to interject that a child's welfare and safety out of school was within his perview and demanded to know what my qualifications were. A little tersely told him I had more qualifications and put them to better use than he did his, that he should restrict himself to seeing that the 3 R's were properly taught, and that I would see to it that my son was raised in a legal, moral and responsible way - he does his homework and plenty of home directed assignments, plays football, baseball + fishes, hunts and shoots. I will not abrogate my authority or responsibility to you.
Went straight to talk to the Superintendent of Schools - had excellent meeting of minds. There is but no question that a message was delivered to the principal as he never again looked at me - he would turn his head away when I came into the school.
Now to be fair, that was over 20 years ago. In the present climate, Social Services might have been called, maybe I'd have to defend against child endangerment charges, and be fighting to get my guns back. That is the sad and ridiculous place we are with some "educators."