Have you considered putting policies on so that they can only log in from certain IP addresses?

What's the email program you are using to retrieve the mail from which the students send the email?

I think I understand your question now. The students log in to register that they are there for the lab, correct?


As for the logging in and out of labs, you might want to create a simple website that records this information but requires that they sign in and out by IP address. As in, they can only access the website if they have an IP from a specific range of IP address. They'd have to record both student name and number.