I'm in need of help! I watched a movie a long time ago, but can't remember the title!

Okay, so what I remember from the movie:
The movie revolved around two boys. One of the boys has a normal home life (I'm going to call him Boy A because I can't remember his name) and befrinds another boy his age (I'm going to call him Boy B). Boy B suffers from a bad home life because he had dwarfism (Or something else that is keeping him smaller than most kids his age). Anyway, Boy B eventually moves in with Boy A (or just stays at his house often). The two boys are playing baseball and the mother of Boy A is hit with a baseball and dies. Boy B blames himself for her death.
After that I don't remember much more, but I rememer part of the end. Boys A and B are on a bus going somewhere, but the bus crashes and Boy B sacrafices his own life to save his classmates and Boy A.

I know this isn't very descriptive, but I'm hoping that someone out there has seen this movie and can help me find the title.
If anyone can help me please do, it will be really appreciated!! Thank you SO MUCH!