Agreed. I learned a lot (and reinforced what I already knew) from tutoring my friend a few years younger than me while they were going through their CS degree. Also learned the value of being patient. Those kind of skills go a long way when you move up the ranks from junior to senior developer.

You think you understand a topic, but you really know for sure when you end up having to relate it to someone else in an understandable form. Helps immensely to reinforce your own learning and tell you what you need to brush up on before meeting with them for a mentoring session.