In my opinion, in general we can tolerate it, but we should not incentivize it, trying to stop it when the case arises.
When multiple persons use the same account and admit it, we should try to convince them to have personal non-shared accounts, both to be in line with the ToS and for their own benefit.
For example, a shared account is weaker than a personal account, a phishing attack on one of the holders is enough to compromise the whole account, possbly losing it altogether.
Or think of two friends parting ways in a non-amicable way, who should keep the account?
For the case in particular, in line with what I just wrote, having a different account for each student would benefit them directly, as they would be free to explore the network and ask their own questions on other SE sites even after they leave the current group and keeping with them the reputation that they might have earned in the meanwhile.
They should be extra careful in not falling foul of the system by upvoting their friends (too) often, but I guess that our moderation team is well equipped for any contingency.