Former New York City Schools Chancellor and noted education reformer Joel Klein and American Federation of Teachers President Randi Weingarten found an unexpected area of agreement. When discussing the future of education at the Aspen Ideas Festival earlier this year, Weingarten noted that she supported giving aspiring teachers a rigorous exam testing their knowledge and reasoning skills prior to licensing them for the classroom. When Klein, along with Delaware Governor Jack Markell, delivered remarks at this week’s Washington Ideals Forum, he pointed out that the teaching profession could stand to be professionalized – by which he meant that each teacher should be subject to a national test akin to the bar exam.

Neither Weingarten nor Klein are the first to propose this kind of licensing exam for teachers. It first gained traction with Albert Shanker, who headed up the AFT in the 1980s, and whose legend endures among those on all sides of education.

When The Atlantic’s Jordan Weissman asked Klein to clarify his statement, Klein said that he was in favor of the exam as well as other changes to the teaching profession because America’s academic success heavily depended on allowing only the best of the best to lead classrooms.

I can see the appeal of the proposal for both sides of the education reform debate. For the unions, as Weingarten said, a bar exam would be a great public relations tool for proving that the teachers they represent are qualified to be in the classroom. It would also inevitably limit the supply of teachers, which might make it easier to bargain for higher wages or prevent competition from charter schools. For reformers like Klein, it might be a step towards attracting a class of talented professionals to teaching who are less likely to want to collectively bargain, and who might be more amenable to ideas like performance-based bonuses.

The exam that Weingarten had in mind – which she described as a “rigorous exam that tests critical thinking and instruction chops” – strongly resembles the massive multi-day bar exam that aspiring lawyers must now pass before they are allowed to practice law. The bar exam is used to make sure that all legal professionals operate at certain minimum professional standards; such a goal seems eminently reasonable when it comes to classroom instructors as well.

Still, those who invest time and effort in obtaining a law license and pass the bar exam do so with the expectation of a certain financial reward, in theory if not – at least at this moment in time – in practice.

Whether or not you’re a fan of professional credentialing — and there are many out there who aren’t — there’s one very obvious problem I can foresee: There’s no way this idea would work unless teacher salaries were raised first, and possibly dramatically. As Klein said, our best and brightest already don’t go into teaching. Throwing up hurdles in front of them without a big payoff in return isn’t going to encourage them.