From Pew Charitable Trust:
A report released by Pew’s Economic Mobility Project shows that community colleges are an important stepping stone for students of all backgrounds, income levels and high school achievements to improve their economic mobility prospects. Earning a community college degree boosts earnings by an average of $7,900 annually, an increase of 29 percent over those with only a high school diploma. For low-income, high-achieving high school students in particular, community colleges serve as a springboard to further postsecondary education; more than half eventually transfer to four-year programs, and three-quarters of those who transfer earn a bachelor’s degree.
Full report (PDF) here.