Kevork Djansezian/Getty Images Jamaal Charles

Before he became an All-Pro running back with the Kansas City Chiefs, Jamaal Charles had to deal with bullying and teasing because of a long undiagnosed learning disability. That enabled him to participate in the Special Olympics as a 10-year-old, and the gold medals he won empowered him. In the latest title from author Sean Jensen's youth series "Middle School Rules," Charles tells his story of overcoming doubters and becoming an inspiration to others. In this excerpt of The Middle School Rules of Jamaal Charles, he is a second grader when his grandmother teaches him a painful but important lesson:

Jamaal is competitive with his brothers and cousins. Since he is one of the youngest and one of the smallest, Jamaal can't beat them in sports. One activity he can beat them in is video games. The boys crowd around the living room television and play John Madden Football, NBA Jam, and Tomb Raider.

But video games bring out the worst in Jamaal ... and his brother ShanDerrick. They yell when a football play does not go according to plan. Sometimes they throw the controller.

"The game is fake," Mom reminds them.

Jamaal falls on the ground and cries.

Middle School Rules of Jamaal Charles "Boy, get off the ground and stop crying!" Mom tells him.

Jamaal is not only crying because of video game disappointments. His brothers and cousins still pick on him because he whines and cries.

At home, Jamaal endures the name-calling and bullying. But at school, Jamaal acts out and misbehaves. By second grade, most students learn to read. But Jamaal struggles to keep up with classmates. They make fun of him.

"What's wrong with you?" Rita asks him. "That's a picture of a dog, so why are you saying door?"

Jamaal struggles to pronounce words and string them together. As he falls behind, he decides to crack jokes. He can get others to laugh with him, not at him. He becomes a class clown.

He disrupts the class by making funny faces and saying silly things. The teacher, Ms. Regan, does not appreciate foolishness in her classroom. She threatens to call Jamaal's home.

"Call my grandma then," Jamaal dares her. "Go ahead and call her!"

"Oooh ..." several students near him say under their breath. Ms. Regan leaves the chalkboard and heads toward her desk in the back. Without saying a word, she looks at her notebook, picks up her red phone, and dials a number.

"Yes, is this Mrs. Miller?" Ms. Regan says. "I am sorry to bother you on this lovely afternoon, but Jamaal is being disruptive in class, and I thought you might want to know."

Ms. Regan pauses, nodding her head.

"Oh, you're going to come to the school now?" Ms. Regan says. "Well, see you shortly."

Middle School Rules of Jamaal Charles - Class ClownJamaal thinks Ms. Regan is not serious.

But 10 minutes later ... Grandma storms through the classroom door, holding a long tree branch. She looks mad. Jamaal sinks into his seat.

"Get up here, Jamaal!" Grandma says.

Jamaal looks around. He wishes there were another boy with that name to save him. But he knows Grandma is there for him, and he knows the switch is not for decoration.

Jamaal slowly walks toward the front of the class. The other students are wide-eyed at what is taking place. When he gets near Grandma, she starts to whip him with the switch and adds, "Don't you act like a clown in class! You know better."

Grandma embarrasses Jamaal. He does know better.

Later, before dinner, Grandma pulls Jamaal aside.

"I know school is tough," she tells him. "But that's no excuse to bother your teacher."

Grandma's Rule: "Act at school the way you act at home."

Middle School Rules of Jamaal Charles - Grandma Quote

Jamaal does not know why he cannot learn like others. Is he not smart? Is he slow? But he realizes he cannot deal with the problem by acting up in class or Grandma will keep spanking him.

What will I do now? Jamaal thinks. What can I do to make the other kids stop bothering me?

-- Excerpted by permission from The Middle School Rules Of Jamaal Charles by Jamaal Charles and Sean Jensen. Copyright (c) 2017. Published by Broad Street Publishing Group LLC. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher. Available for purchase through Amazon, Barnes & Noble, iTunes and Google Play. Follow Jamaal Charles on Twitter @jcharles25. Follow Sean Jensen on Twitter @seankjensen.