When they put their newspapers down and open their books, it's Sophomores. When they look up so they can see the instructor over the tops of the newspapers, it's juniors. When they put their feet up on the desks and keep reading, it's seniors. When they write it down, it's graduate students. It looks like they're finished.
Teachers do it with class.
Teachers do it 50 times after class. Teachers do it with boys and girls. Anything not completed during the lesson is added to the homework. Light bulb changing isn't in the course notes. But several days later when she announced she had won a third contest, she was somewhat subdued.