It's a juvie, which is what Young Adult (YA) fiction was called back when Heinlein was writing for that market. However, I called it a 'juvie' because the book

It's a juvie, which is what Young Adult (YA) fiction was called back when Heinlein was writing for that market. However, I called it a 'juvie' because the book fits the older style better: A young person Gets Into Trouble and uses Native Wit, Loyal Friends, and a few Helpful Adults to Solve The Problem. It not incidentally teaches Moral Lessons by example, like how important it is to stand up for yourself and so on. Modern YA stuff is more psychologically deep and less focused on Solving The Problem. Anyway, the target audience is middle school to high school. The protagonist is in high school, but it's a rule in kid lit that kids will gladly read things meant for older kids but never stuff meant for younger kids.