Roughly half of American jobs require education greater than high school and less than a full four-year degree, making them "middle-skill jobs."
For example, in the graphs to the right, the middle category includes sales and related occupations, office administrative support, construction, installation and repair, production occupations, and transportation and material moving. They're a smaller share of the total than they were in 1996, but they're still huge.
America's Forgotten Middle-Skill Jobs: Education and Training Requirements for the Next Decade and Beyond (published in 2007 and available here) argues for education strategies that build a workforce ready both for high-skill and middle-skill jobs.
The Council on Postsecondary Education's big goal is to double bachelor's degrees in the workforce by 2020, without a separate target for associates and certificates.
Reports like this argue against that exclusive emphasis, contending that the economy needs workers with a range of postsecondary skills and we need education strategies to match.