I'm a bit late getting to this one, but it's a report of an interesting study (abstract here) that finds:

Low-income youth are more apt to vote if they are involved in political activism, according to a new study that also notes the influence of friends and family.

This is a fairly understudied population -- hard to reach, hard to get to participate, and often with less political power (thus, less interest in those who pay for surveys and other forms of research).