Tremors erupted in Southern California a few weeks ago. The epicenter of the shake-up is in Los Angeles, but the tremors are being felt around the country.

Rather than tectonic plate tension along the San Andreas fault, the rumbling in California was caused by the publication of teacher evaluations by the Los Angeles Times.

The Times analyzed seven years of data for math and English test scores, examining how much a given student's score improved or declined from year to year. This method of evaluation is called value added and has become part of the controversy.

The reaction from many teachers and the teachers union has been negative. The Times headline yesterday reads, "Teachers blast L.A. Times for releasing teacher effectiveness ratings."

The teachers union, the United Teachers of Los Angeles, said in a press release, "It is the height of journalistic irresponsibility to make public these deeply flawed judgments about a teacher's effectiveness."

While it is true that the value-added method is not perfect, it does, however, offer some insight into a teacher's effectiveness. Clearly, it does not tell the whole story, and not even the supporters of the value-added approach suggest it should be the only tool used to evaluate teachers.

One expert defended the system, saying it was good at identifying the small group of teachers at the top and at the bottom of the effectiveness scale. The problem comes when looking at strict numeric rankings of teachers in the middle of the bell curve of effectiveness.

But it doesn't really matter to know precise rankings in the middle, where most teachers will fall, to see that teacher Bill Smith is ranked 175 out of 600 while teacher Mary Jones is ranked 203. What's important is identifying those in the top 50 and those in the bottom 50.

Identifying those teachers at the top so that they can possibly serve as mentors to help other teachers improve is important. It's also important to identify those teachers at the bottom of the scale, so that they can be offered help to improve their effectiveness. But if that fails, those subpar teachers should be removed from the classroom — without unreasonable resistance from the union.

Precise rankings of every teacher are not important and should not be used to discredit the value-added approach.

Clearly, other factors including classroom observation by principals and other administrators should also be factored into evaluations of teachers.

In Los Angeles, the school district wants 30 percent of a teacher's evaluation to come from the value-added scores, but have the larger portion of a teacher's evaluation based on classroom observations.

Some teachers and union officials argue that the public has no right to see teacher evaluation data. But few people — taxpayers or parents — would agree with that position. The public, which is paying the teachers' salaries, after all, should know as much as possible about teacher effectiveness, and what districts are doing to improve the quality of the teaching staff.

Not all teachers are equally effective. That's true in any profession. Yet teachers unions resist efforts to identify those who are the weakest so that they can get help, but face removal from the classroom if they do not improve.

Teachers unions claim to be all about the students. If that were true, unions would not resist evaluations leading to a culling of the least-effective teachers.

The publication by the Times of the teacher evaluation scores is serving the public interest. At the very least, it is beginning a serious debate about the best ways to evaluate teachers and elevate the quality of professionals in the classroom. That's something that would serve the students' best interests — in Los Angeles and everywhere else across the country.