May I go to the toilet, please?

My students were having mid-term exams. They had to concentrate on the exams during that week. In the exam room, everybody had to do the tests seriously. Some subjects needed much time to do, but some of them needed only a short time. Usually we have 90 minutes for each subject, except for Maths.

That day the students took a test of Computer theory. All of the students in my class
needed only 45 minutes to do the test. After they finished doing the test, they did nothing...and they became bored....

One of them came to me, asking for permission, "May I go to the toilet, please?" "No."

It was easy to give permission to him, but it's not about the permission. I didn't give permission since I wanted my students to be good students. First, they should learn to manage their time - when they can go out of the class. Second, they should learn not to disturb the concentration of other students in their class or in other classes. Third, they learn to conquer the boredom they feel. In 90-minutes boring situation is not hard for them. They're strong enough to handle the situation...but why do they give up???