If the Democratic race is settled at the party’s convention this summer — not unlikely, given Hillary Clinton’s victories over Barack Obama in Ohio and Texas — certain delegate constituencies are going to be the object of much affection from the candidates. Most prominent among these is the delegate and superdelegate bloc affiliated with the National Education Association and the American Federation of Teachers, the nation’s two largest teachers’ unions. In 2004, more than 400 regular delegates to the convention were members of the two unions, making up a group bigger than every state delegation except California’s.

Good news for the unions, however, might not be good news for American education. The union agenda has often run counter to the interests of students and teachers alike.

Take those collective bargaining agreements that the unions have negotiated in school districts across the nation. As Terry Moe, a professor of political science at Stanford, demonstrated, these agreements have hampered student performance in California. Why? Because they protect ineffective teachers — at the expense of everyone else.

Or consider performance-based pay. Forty percent of teachers leave the classroom within their first five years on the job — in some measure because they don’t stand to gain the same performance-based pay raises available to their private-sector counterparts. Merit pay would make it possible for public schools to retain good teachers by paying them more. But the unions have fought against such measures.

The same can be said about school choice. Despite compelling evidence that it improves student achievement, the national teachers’ unions regularly stand against the policy.

The list goes on. While politicians are aware of the consequences of having these unions set educational policy, they are also aware that they have millions of members and dollars at their disposal. At a convention where every vote is in play, that union power has the potential to be greater than ever before.

A brokered convention sounds great. If, however, the brokers happen to be the teachers’ unions — unions that have never been shy about extracting promises — the outcome could be an unhappy one, at least for public education.