WHAT’S the key to success in the United States?

Short of becoming a reality TV star, the answer is rote and, some would argue, rather knee-jerk: Earn a college degree.

The idea that four years of higher education will translate into a better job, higher earnings and a happier life — a refrain sure to be repeated this month at graduation ceremonies across the country — has been pounded into the heads of schoolchildren, parents and educators. But there’s an underside to that conventional wisdom. Perhaps no more than half of those who began a four-year bachelor’s degree program in the fall of 2006 will get that degree within six years, according to the latest projections from the Department of Education. (The figures don’t include transfer students, who aren’t tracked.)

For college students who ranked among the bottom quarter of their high school classes, the numbers are even more stark: 80 percent will probably never get a bachelor’s degree or even a two-year associate’s degree.

That can be a lot of tuition to pay, without a degree to show for it.

A small but influential group of economists and educators is pushing another pathway: for some students, no college at all. It’s time, they say, to develop credible alternatives for students unlikely to be successful pursuing a higher degree, or who may not be ready to do so.