Freak the Mighty can definitely be enjoyed by Shmoopers of all ages. But it's got the trademark YA characteristics:
(1) It's about an 8th grader—i.e., a young adult.
(2) The language is pretty simple and probably intended for a younger audience.
(3) The word butthead is repeated like a thousand times.
Over the course of Max's 8th-grade year, he has to deal with things that would change anyone—not just an adolescent. Let's take a look:
• He finally has to face the events surrounding his mother's murder.
• His father kidnaps him.
• His best (and only) friend dies.
It's no wonder Max comes out the other side a totally different person. But Max's most significant growth revolves around how he views himself: he finally realizes that he's more than just a "butthead" who lives in his grandparents' basement. And maybe, just maybe, he might be smart. Just like Freak.