Another part of being a student is trying on hats. How can you know what you want to do with the rest of your life if you don't do that? Working professionals may do this too, but probably will do less of it than students. If a working pro commits to a voluntary activity, the commitment is ongoing. As someone said yesterday in class, student status is by its nature temporary. Many student commitments end with graduation and a change in location as the student enters the workforce or enters graduate/professional school. This experimental motive would tend to make students volunteer more than working pros.
In contrast, the presumed ongoing presence of the working pro on the job and in the community where the working pro lives encourages voluntary activity that improves quality of life in these locations. That incentive is much weaker for students, who are in a transient state for the most part regarding their residence. On this point, there may be substantial gender differences. With young kids at home, many families might prefer that work is part time. Finding good part time jobs is hard, however. Barring that, one spouse might continue to work full time and the other withdraw from the world of work for a time. That decision is definitely not gender neutral. Then, the stay home parent might look to volunteer, in part, as a way to diversify the set of activities, to interact with other adults, and to improve the environment where the kids go to school. Once these behaviors are learned, they may continue well after the child care needs have been dramatically reduced or eliminated entirely.
One motive that seems similar for both student and working pro is the volunteering for the credential. Participating in a professional organization in a way that is visible to one's boss or to one's potential future employer is similar if not identical to student volunteer activity that helps on a application to grad school. There is perhaps a small difference here in that some of this sort of activity for the working pro takes them physically away from their job and hence requires approval by the person the working pro reports to. So there is some organizational embrace of the volunteer activity (which means it is a little less like volunteering). But otherwise, the motives are similar.
However, there is an aspect of the participation in the professional organization that really is not replicated with students, which is a kind of giving back so the next generation have it as good as the current generation. This reason to volunteer as an extension of the work we do, requires being a mature pro. It is a tribute to the experience already obtained.
I've written this up to expand on the discussion in class yesterday. Drucker focuses exclusively on volunteering that is not an extension of work, but is apart from work. He also seems to focus on paid work that is not of the service kind - doctors, social workers, teachers, etc. One might wonder whether those whose job is service oriented also volunteer in activities that are apart from work.
I believe you can get more out of what we discussed in class yesterday, and out of Drucker, if we keep these sort of distinctions in mind.