That is, in a YA novel, if the problems are not adolescent in scale (what courses should I take? etc.), but threatening anything from the school to the world, the adults must be absent, incompetent, or evil. Because there needs to be some reason why they aren't intervening in the problem when the person trying to face it so young.
Well, unless the youngster is in a supporting role in the main conflict. That is possible, hard to pull off, and not really feasible for my current work-in-progress.
I haven't had it before -- even in A Diabolical Bargain, the hero's in college, not secondary education -- but this involves a boy in his last year of secondary education. A fair amount of leeway, but he is facing a grave problem.
Somewhat assisted by the way the youngsters (our hero and some younger ones) are shuffled off to somewhere safe. Somewhat hindered by the way they actually are trying to keep them safe.
I think the hero's found a spell that will let him get into the thick of things.