One of my astronomy students was in my office hours, taking a makeup exam today. I reserve the right to not give makeup exams, and this student admitted that he did not have a good excuse to miss the exam. However I decided to let him redeem himself. As he was taking the exam, one of my physics students came in to ask questions. The physics student explained that he'd arrived at the library at 7am to read the new chapter in advance of class today. He'd also started on the homework and had a few specific questions about them. We also cleared up a question that we had corresponded about via email over the weekend. The physics student thanked me, and then he left. About 15 minutes later, the astronomy student finished his exam and then told me he was sorry. He said that hearing what the physics student was doing made him realize that he could work harder. He was going to tell his friends (!) what he had heard, that there are people who actually work that hard. He just kept shaking his head, as if he'd been truly jolted.
I'm thinking this might be the best bit of peer instruction I've ever seen, and it was completely unintentional. I hope this astro student really will work harder, in all of his classes. Sometimes it is best to sit back and let the students teach each other, eh?