There has been a recent study of the post-corps experience of Teach For America teachers. They discovered that TFA teachers are not significantly more involved in voting, charitable giving or civic engagement. The poll takers credit the disappointing results to burnout and disillusionment. Thankfully, a former TFA teacher has shown some problems with the poll's numbers.
Since I can't find the poll on-line, I also wonder if it was measuring the wrong things. Among TFA alumni that I know, I notice a difference in their attitudes toward community change. Their young idealism has often given way to a tested and mature realism. They are still committed to solving inequality and injustice, but they have learned how to work within existing institutions. They are imaginative, but they are also pragmatic. Most importantly, many have also learned patience. The fight for justice is a marathon, not a sprint.