WHEN I was in school a well-meaning teacher thought it would be an excellent idea to bus us teenage girls to a local prison each week to volunteer. We tutored prisoners for the GED, an exam taken by people who drop out of secondary school. It is widely regarded as a high school equivalent. There exists a lot of evidence that completing high school increases life-time earnings. So drop-outs are often encouraged to take the GED. (There are many government programmes that subsidise preparation for the exam, especially for prison inmates.)

The GED has grown in popularity since its introduction nearly 70 years ago. It now makes up about 12% of high-school certifications. But the GED is not really a high-school equivalent. The performance of GED takers on a scholastic achievement test may be similar to someone who finished high school. But according to a new paper, GED recipients do not earn more than drop-outs who don't take the exam. The GED takers do have higher rates of college matriculation, but most drop out after only one semester. The problem is high school drop-outs tend to have less self-discipline, are more impulsive and have lower self-esteem and self-efficacy than people who finish high school. A high-school equivalency exam does not fix these non-cognitive deficits.

You could argue that even if the GED does not really change labour-market outcomes, it provides a positive goal and imparts some sense of accomplishment to an at-risk population (and let's be honest, you have lots of free time when you're in prison, so there exists only a small opportunity cost to preparation). The inmates I worked with took pride in the exam, and passing it may have helped their self-esteem. But the authors of the paper argue that the growth of the GED programme has actually been quite damaging. First, it masks the extent of the educational disparity between blacks and whites. If you don't include GED takers in educational attainment measures, the high-school drop-out rate has not improved since the 1960s. Counting GED recipients as high-school graduates also over-states the income benefits of college.

The authors of the paper contend the GED was sold as a quick fix, but does not address the real problem: America's education system continues to fail poor, minority students. Many of the characteristics that keep drop-outs from succeeding need to be addressed in early childhood and are caused by deeper social issues. There's also evidence that the very existence of the GED may encourage drop-outs, because people figure they can obtain an equivalency later.

But even if these complex problems were addressed, some people will fall through the cracks and be left without adequate training. The inmates I worked with certainly had deeper issues, which explain why they were in prison in the first place. Having a positive goal like the GED seemed useful, but I often wondered how studying biology could help them after release. Perhaps focusing on vocational skills for drop-outs and prisoners would be a better use of their time and government resources. That would not fix all their problems either, but providing them more applicable skills may save some future frustration and disappointment.