The truth is that if American high schools (and middle and elementary schools) were doing their jobs, many students could get all the formal education they need in 12 years. In any case, we need to move from a ‘time based’ to a competency based educational system. You don’t get a high school diploma because you have spent 12 years in classrooms; you get a high school diploma because you have demonstrated a certain level of core competence.
James Joyner, along the same lines, wants to shorten college:
There's no reason an undergraduate degree should take more than three years unless the student is working his way through school and can't devote full-time energy. A master's degree should take a year and a JD two. The PhD has gone from a two- or three-year program as recently as the late 1960s to a five- to seven-year program almost solely on the basis of keeping grad students around as cheap labor. Accelerating the process would do wonders in curtailing the skyrocketing cost of higher education. I’m not sure, though, how it would help with the problem of students who aren’t ready for college.