I adored this book as a kid. I also grew up in the town Twin Mills is based on (Jerry Spinelli's hometown, Norristown, Pa.) and I can guarantee you that the people who made the movie have never been to Norristown. They probably didn't even read the book.
It was much, much too happy and shiny with no sense of its story or setting. Norristown is a bleak town divided by racial tensions; the story of Maniac is one boy making a difference. The movie is a trite little piece of shiny Nickelodeon crap.
All in all, I can't recommend avoiding this movie enough. Just read the book to your kids, and while you're at it, read Dump Days, an excellent companion.