http://physorg.com/news4333.html
I've seen a good deal of this in my own household. Getting my sister to do homework is a furious battle for my parents. I went through a stage in 4th grade where I just didn't do homework, and I failed English because of it. It's not that I didn't know the stuff, I didn't like homework and having to read hundreds and hundreds of pages each month. And of course, I still don't like doing homework and I quite often don't. If I don't understand a concept I'll read up on it and maybe do a few problems from a book.