I'd say it boils down to simple respect for other people's time and your own time. The professor is up there spending their time teaching. The students are in a

I'd say it boils down to simple respect for other people's time and your own time. The professor is up there spending their time teaching. The students are in an learning environment which a number people have spent their time (or lives) constructing. In addition, by choosing to enroll in the class or in the college the students have agreed to invest a portion of their time learning. Completely ignoring the class and doing something else on a laptop or phone says that the student in question believes the course or college is a waste of their time. While that may be a valid point to make, I feel it is cowardice to make it by ignoring the people around them. It could just as easily be made by letting everyone know they think the course is a waste of their time and then leaving the course. Even better, they can stay and try to improve it. This way the people who are interested in the course can continue it in an environment where everyone is actually interested in the course. From my experience, something as simple as having everyone paying attention makes a large positive difference in how participatory and enjoyable a course can be.