My wife is a grade school teacher, and would largely back up your roommate's theory. She finds, though, that there are some parents who are heavily involved, but usually in making excuses for their child. Every year there are 1 or 2 like that - I usually start hearing the names early in the year, and know I will hear them repetitively the rest of the year. And those kids usually don't do well - the next year's teachers find them just as bad as my wife does.
On the other hand, the majority of parents who are involved with their child's schoolwork do quite well.
Drew Garrett
As a teacher, I agree with the parental involvement theory, too - with Drew's wife's modification. And, I find it works regardless of race or socioeconomic level...