Mr. Jack Is a Maniac is the tenth book in the My Weirder School series.
A.J. and the Ella Mentry Elementary School gang learn some unusual self-defense moves from a wacky teacher who thinks he's an action hero
The book begins with AJ beginning to have a hatred for hate. On a nice day on the playground, Dr. Brad talks to AJ's class about kindness and tolerance. He explains to them that if they have a disagreement with someone, they should try and talk it out instead fighting about it.
They walk into the woods and hear a noise in the trees. Suddenly, a big black motorcycle comes speeding out of the bushes. It stops in front of Dr. Brad, and the driver takes off his helmet and introduces himself as Mr. Jack. By then, a whole bunch of kids and teachers see the motorcycle and run over to meet Mr. Jack.
Dr. Brad tries to explain to Mr. Jack that he needs to leave school property. He then summons a few male teachers to get rid of Mr. Jack. But just as Dr. Brad is about to demonstrate honest discussions, Mr. Jack picks up Dr. Brad and throws him across the playground. Mr. Jack then beats up Mr. Macky, Mr. Granite, Mr. Loring, Mr. Docker, Mr. Louie, and Mr. Tony.
In the middle of the commotion, Mr. Klutz comes out asks what's going on. Mr. Jack then challenges Mr. Klutz and beats him up. Dr. Brad then tells the class that Mr. Jack's fight with the teachers isn't real and that they should settle their differences with words instead of violence. Mr. Jack tells the kids that he will teach them some self-defense moves in case of an emergency.
In the gym, they warm up with a few exercises and a meditation exercise. After they are done with the exercises, they get ready to learn self-defense. Mr. Jack tells the kids to put on helmets, kneepads, elbow pads, and other body protectors. They then seal themselves up in bubble wrap. Once they start, AJ tries to beat Andrea, but she grabs him and flips him over. Then she twists his arm and elbows him in the stomach. AJ tries to not get beat up by Andrea, but she kicks him in the head and he falls backwards into the bleachers. Andrea tells Mr. Jack that she takes karate classes after school, which explains why she's so good at beating people up. She then tackles AJ, much to his horror.
When AJ is back in class, he feels embarrased because he got beat up by Andrea with his classmates watching. During another session with Mr. Jack, they learn how to get out of the way when fighting by dodging ping-pong balls. Eventually, AJ manages to survive and wins the game. After the game ends, Mr. Jack talks about intimidation. He demonstrates by stomping around and waving his jacket in the air.
When they get back to class, Mr. Granite tries to start a lesson, but Mr. Jack comes in and tells the class that they need to prepare themselves when they get attacked. Then Ms. LaGrange comes in with a large block of ice. Mr. Jack explains to them that in order to defend themselves, they need to look tough. Mr. Jack demonstrates by attempting to break the ice block in half with his head, but his attempt fails when the class gets an announcement that they have to go down to the gym.
In the gym, Mr. Klutz says that everyone did a great job with Mr. Jack, so he will hand out certifiacates and tells them that they need to use self-defense for emergencies only. Suddenly, a large black bear comes into the gym, scaring everyone in the process. Dr. Brad tries to be reasonable with the bear, but the bear picks up Dr. Brad and throws him across the gym. Mr. Jack doesn't know how to beat up the bear even though he's an expert at self-defense.
The kids then realize that they need to intimidate the bear by themselves. Andrea karate-chops the bear and AJ dives out of the way when the bear tries to claw him. The kids then decide to join in. They use karate moves to attack the bear and they dodge out of the way when the bear tries to claw them. They stomp around waving their jackets. The bear then gets so intimidated, that he walks out the door. Everyone celebrates and Andrea kisses AJ, which, to AJ, is more intimidating than the bear. Then AJ thinks of the things that happened previously in the book and wonders what might happen next.