Jordan Shapiro's Temple class delved into a weighty discussion of Plato's allegory of the cave. On the classroom wall flashed a series of posts on Twitter. While many professors ban tweeting in class, Shapiro encourages it. In fact, he was very happy when a student texted with a friend about the class discussion. "Socializing about Plato? Is there a better thing? That's how they're using their phones," Shapiro said. "I felt completely validated."