Summary from Goodreads:
Starting at a new school is scary, even more so with a giant hearing aid strapped to your chest! At her old school, everyone in Cece's class was deaf. Here she is different. She is sure the kids are staring at the Phonic Ear, the powerful aid that will help her hear her teacher. Too bad it also seems certain to repel potential friends.
Then Cece makes a startling discovery. With the Phonic Ear she can hear her teacher not just in the classroom, but anywhere her teacher is in school--in the hallway...in the teacher's lounge...in the bathroom! This is power. Maybe even superpower! Cece is on her way to becoming El Deafo, Listener for All. But the funny thing about being a superhero is that it's just another way of feeling different... and lonely. Can Cece channel her powers into finding the thing she wants most, a true friend?