This is not a war on teachers en masse. It is recognition of what every parent knows: Some teachers are exceptional, but a small number are dreadful. And if that is the case, we should think of ways to change the balance…

There is a place for an enlightened union that accepts the simple premise that teacher performance is an integral part of effecting reform. As the late Albert Shanker said in 1985, when he was president of the American Federation of Teachers: “Teachers must be viewed . . . as a group that acts on behalf of its clients and takes responsibility for the quality and performance of its own ranks.”

The bottom line is that focusing on effective teachers cannot be taken as a liberal or conservative position. It’s time for the unions to drop their polemics and stop propping up the bottom.

Eric A. Hanushek in today’s Wall Street Journal.