To be honest, it depends on how responsible a student is. I myself is a still a student who relies in Bitcoin to help me finance myself but I for once haven't forgot about my studies and had an average grade of B+. You should consult your students and approach them to give them some advice. It's not Bitcoin's fault but it was students entirely. 
I agree with you. Nowadays, college students have a lot of spare time. As long as they can allocate reasonably, they should not spend all their time investing in bitcoin, which will not affect their studies. And by doing some bounty activities for rewards, so you can earn their living expenses.