Book about a boy who is trying to get superpowers?

There’s this book that was published before 2011. The main character narrates the story. He tells the audience that if he doesn’t get superpowers by his XX birthday, then he never will.

The story begins on the very last day of that time frame. The first chapter begins with him testing himself for superpowers, and he finds nothing abnormal. He goes to a school for superheroes, and a lot of his classmates already have superpowers. He arrives at his first class. The school then experiences a life-endangering commotion, but I forgot what it was exactly.

At this point, I’m not confident in my memory. Some of the details below may be inaccurate.

Since he didn’t get superpowers, he will have to transfer to another school. All of the students are waiting for the teacher but the teacher never shows up. Some creature attacks the school, and students from another class are fighting off the creature. There was this "cool kid" (popular? showy?) from another class that tried to take charge of the situation. The commotion creates a big hole in the classroom wall. The main character and his friends step into action.

That’s all I remember at the moment. Some details that might help:

• This book, or at least an excerpt, was absolutely published before 2012.
• There’s a small chance that I read an excerpt of this book in a compilation of stories, such as the Guy’s Read series.