Old School, by Gordon Korman

For the past six years, Dexter has been raised by his grandmother and the other residents of The Pines, a retirement community.  Being the youngest permanent resident, he's been doted over by the old people.  School?  He is getting all the schooling he needs from the various talents residing here.  But when a truant officer shows up, Dexter is told that he'll have to go to a real school, with kids his own age.

He hasn't socialized with anyone like that in ages and his first days of middle school are rough. He is singled out and bullied for his old-people clothes and his old-fashioned way of speaking.  But slowly he reveals his own particular contributions and makes friends.  Then, an unfortunate incident leads to his suspension and suddenly he and his classmates realize just how much Dexter actually does belong in school.

A cute story that suffers from the author's peculiar perception that the residents of The Pines are a lot older than would be normally plausible.  He hasn't populated it with a twelve year-old's grandparents but with the author's own grandparents.  Sorry, but old people don't listen to Benny Goodman and talk about the Great War anymore.  They listen to Jefferson Airplane and talk about Vietnam.  They are not the Greatest Generation, they are Baby Boomers.  It's cute having the old people teaching the kids to play bingo and shuffleboard, but its a dated stereotype.