For one, you create your own expression. Yes, the whole class is working in clay, but I'm not doing the same things as the kid next to me. In fact, it's far better that I don't do what the kid next to me does. I can express freely what I wish to express.
Even greater than that at some times, though, is the freedom of thought during class. In Japanese, I have to focus on the questions and answers, in politics, I focus on the lecture and take notes. In art, my mind can go whenever I wish it to wander. I can focus on mixing my clay, and then, slowly, let it drift to wherever. When I need to bring myself to focus on a particular aspect of the work, I can do that, and then, return to day dreaming. Often if I'm caught up in a project, that will be rewarding enough, but on more mundane tasks, I have a reprieve from the boredom.
Working in clay almost makes up for that whole newspaper fiasco.