The document discusses different types of classroom exercises and their effectiveness for student learning. It lists 6 examples of exercises, ranging from students working individually on a computer exercise to the teacher demonstrating a chemistry experiment. It then ranks the exercises from less effective to more effective for retaining knowledge, with individual, pair, and group work ranked as more effective than teacher-led demonstrations or lectures. The document goes on to discuss challenges and opportunities teachers face in incorporating online learning and technology into their lessons.