The most fulfilling part of my experience has been getting to know the kids and seeing them progress over time.

Working with them individually allows you to see how they're adapting and growing — even over the course of several years.  This also allows you to get to know them as people, and to see how sweet, funny, and hard-working they are.  It's also interesting to get a sense of how the little we goes a long way and helps create a positive impression for new volunteers.