Classwork is the work students do in the classroom while the lesson is happening — exercises, questions, a short piece of writing — not the work they take home. Teachers set it beside homework: one stays in the room, the other goes with you. Though actually, the line can be a little soft. Some classwork is started in class and finished later, and some teachers still call that classwork. It is a school word, used by teachers, parents, and students. You would not use it for work in an office.