In 2007 Comverse required a bit of help with the training of a junior programmer.
I personally helped one of the junior developers build out a file synchronization tool. This involved daily mentoring sessions, code reviews, and paired programming sessions. This was extremely fulfilling as the developer was really inexperienced and was basically forced to sink or swim on their own. This project went on for a few months and by the end of the time the developer was comfortable with continuing on with the development of this tool on their own.