The Obama administration is proposing a program that seems simultaneously completely obvious as a matter of policy and completely impossible as a matter of politics: Why not subsidize college education for prisoners?

The benefits are clear: Research suggests the program could cut prison reentry and, as a result, the overall cost of prisons. And if the point of prison is to take criminals and make them productive members of society, helping them afford the education needed to win a good job after release seems almost core to the mission.

But the politics are difficult. For the past two decades, Congress has banned prisoners from receiving Pell grants to pay for college. After all, who wants to reward someone who committed a crime by paying for their college courses?

The new three- to five-year pilot program will offer Pell grants to prisoners who are set to be released in the next five years — although some details, including which colleges will participate and how many prisoners will be eligible, need to be worked out. The goal, officials said, is to use the pilot program to gauge whether the decades-long ban on prisoners receiving Pell grants should come to an end.

The problem is taxpayers are already spending money on prisons and their inmates. The question is how to make that spending more efficient and effective, and whether Pell grants could do that.

Paying for prisoners' college education could save taxpayers money

The most authoritative research on how education can benefit outgoing prisoners was done by the RAND Corporation in 2014.

The study looked at how education programs — not just college, but all efforts — can help address a big problem in the US: 40 percent of incarcerated individuals who leave federal and state prisons will commit new crimes or violate the terms of their release and be reincarcerated within three years. This is bad not just for the person being sent back to prison, but for the taxpayer — prisons are already crowded and costly, and any extra inmate adds tens of thousands of dollars in costs.

Ideally, an education can help solve this problem: A high school and college diploma make it easier for inmates to find a job, so they won't have to turn to crime to make ends meet once they're out of prison.

Every $1 spent in correctional education programs translated to $5 saved in prison costs

The RAND study backed the idea. It found that inmates who took part in education programs were 43 percent less likely to return to prison within three years of their release than prisoners who didn't participate in the programs. And that meant big savings for taxpayers: Every $1 spent in correctional education programs translated to $5 saved in prison costs, RAND estimated.

The study comes with a big caveat: It's really difficult to research the effectiveness of these programs due to selection bias. The prisoners who sign up for and attend voluntary education programs are likely the people who are already most likely to succeed, since they're showing a drive to improve their situation once they get out of prison just by signing up for classes. The RAND study employed several controls to reduce the impact of this selection bias, but it's impossible to rule out completely.

The research also included high school and more basic education, which goes beyond the reach of Pell grants, as they only fund a college education. So RAND's numbers don't represent the exact gains for just the Pell grant program.

Still, the findings suggest that education programs in general reduce the likelihood of prison reentry. And for taxpayers, that likely means savings.