The problem is not the students themselves, but that their circumstances make them a flight risk. If you encourage people to start a startup as an alternative to a summer job during college, they won't be very committed to it, and commitment is the most important thing in a startup.
The moment someone graduates, this problem goes away, because then all the social pressure switches to encouraging them to work on the startup, instead of encouraging them to go back to school.
From my two years at university, I've had interesting conversations with friends specifically about starting something.
Here's the problem: from what people hear in the media, college folks have this idea that START UP = GET-RICH-QUICK. And on that basis, it is not hard to get someone to be your cofounder. Of course, then I explain to them that while this could make us really rich, it also has tremendous risk and that I start start-ups FIRSTLY because it is my passion before anything else. At that point, almost everyone I know just finds it easier to maintain their good GPA instead of risk their GPA and degree for a start-up.
A good test I have is asking someone what they would do if they are taking an exam and find out midway through that their high traffic server and website is down.
The moment someone graduates, this problem goes away, because then all the social pressure switches to encouraging them to work on the startup, instead of encouraging them to go back to school.