From the University of Missouri at Columbia Career Center:
Volunteering is an experience that provides the opportunity to give time and energy to a worthwhile cause. It is for those who believe that they can make a difference in the lives of others through the application of their special talents and efforts. Service Learning takes volunteering one step further. It involves meeting the same needs that volunteers do, but it is combined with conscious educational growth. Service learning is a chance to learn (and possibly earn some college credit) while helping to better the community.