I agree about the issue of motivating students, but I think Andrew's right. The idea is that it needs to be clear an assignment is an assignment. While I was an undergrad I was a teaching assistant for a class with a service-learning requirement and the first day we spent a lot of time trying to explain to students that the expectations of meeting this requirement was no different than any other assignment. Meeting with the community partner was no different from any project requiring a group meeting or a trip to the library. Even that paying for a couple of bus trips to and from the partner site was no different from paying for printing class materials or buying other school supplies. I agree that not all students followed through, but we found we were more successful when we had this discussion outright and took the time to explain how the experience could benefit them. Eventually, the school was also able to get a code designating these service-learning courses in the registration system to further highlight the requirement when students decide to take the course.