Strange, cheerful kid with a digestive problem [s]

[Rosa]

This is a young adult novel about a boy who may be supposed to have some kind of disability, such as Down syndrome, or may just be unusual. He has a valve in his stomach turned upside-down for half the book (until he gets surgery for it) and consequently throws up all the time as if it's nothing. Once he threw up in the mail bag of his father, who is a mailman. He is very proud of his father's career and once went on his rounds with him as a junior mailman, during which he met a lonely old lady his father always says hello to.

In elementary school the boy is teased, but in junior high he stops being teased because he fades into the background. He has only one friend. The novel ends from the perspective of someone else, watching the boy playing softball or kickball, nonplussed by how cheerful he is while being so terrible at the game.

[Rebecca]

I believe this is Loser by Jerry Spinelli.

Excerpt:

"As his father gets out of the car, Zinkoff runs to him, plunges his head into his father's mailbag and throws up.

Zinkoff was born with an upside-down valve in his stomach. This causes him to throw up several times a week. To Zinkoff, throwing up is almost as normal as breathing."

[Rosa]

Hey, that's it! Thanks for the quick answer!

[Rebecca]

Glad I could help!