Taking a belt to him won't solve anything, and will probably just make things worse.
My youngest son was having a similar problem, and homework monitoring was the answer. Check with his teachers to find out what his assignments are going to be, and make sure they get done. Missing assignments get privileges removed (my son had video games, then computer, then tv privileges removed). My son went from Ds and Fs to As and Bs with this method. It's HARD, though, because you have to follow through with every single assignment. It only took about one school year, and now I don't have to babysit him at all, and he's proud of the grades he brings home.
Everyone else is right too... there could be an underlying problem like bullying. It's hard to concentrate on school when someone is beating the crap out of you every day.
Make sure there are no medical or vision problems, either.
Kaessa - Geek Grandma
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"In other words... if what I type doesn't make sense, I blame the meds."