Should kids work while they're in college?
First, there's a procedural issue: For any money that a college student earns over $4,000, 50% is deducted from any financial aid he would otherwise receive. Is that fair? No, it's idiotic. But that's the way the system works and it means that if your family qualifies for need-based grants, it may not be worth it for him to earn more than that -- until after filing the FAFSA form for senior year. After that, it doesn't matter.
So you have to factor that in but assuming it might make sense for him to at least work some, the question is how much. According to Money, "An American Council on Education analysis of several studies indicated that students who work more than 15 hours a week are less likely to graduate in four years, which means even more tuition to pay."
But I wonder how much of that is a selection bias issue: A lot of students who work full-time do so while attending college part-time or otherwise planning to stay in school longer. It's a matter of priorities: I'm currently a college sophomore and I have a hard time believing that anyone is so busy studying they couldn't work 20 hours per week -- some students will cut studying time instead of partying time, but that's an issue of the student's personality and persuasion. Motivated, ambitious kids can work their way through college and still perform well.