Embarrassed by a Los Angeles Times story revealing teacher tenure has been all but automatic in Los Angeles Unified, the district is tripling the number of probationary teachers who will be fired this year.

The extra scrutiny will help weed out bad teachers before they gain due process rights that make it very difficult to fire teachers for poor performance. But L.A. Unified’s ability to identify effective teachers is still hampered, as in many districts, by a poor evaluation process and a problematic, two-year probationary period. The district is in the process of changing the former, but only the Legislature or voters can fix the latter.

The 110 teachers who will be let go will comprise only 6 percent of non-tenured teachers, according to the Times. That’s hardly a purge or an overreaction. But it will represent triple the average of 35 probationary teachers dismissed each year .

With substantial layoffs expected in Los Angeles and other districts this year, it’s critical  to  protect future star teachers through effective evaluations. Better still would be a system of layoffs based on effectiveness in the classroom, not seniority. Gov. Arnold said he would  prod the Legislature to change state law – a move that the state’s teachers unions will fight.

In many districts, new teachers are  evaluated primarily on several observations, often cursory, by the principal. L.A. Unified has appointed a task force, chaired by state Board of Education President Ted Mitchell, to revise the evaluation process, perhaps to include peer ratings by teachers.  In signing up to participate in the state’s Race to the Top application, school districts agreed to consider including student test scores as a factor in teacher evaluations.  But the terms must be negotiated on a local level.

All of the teachers who will be fired got one or more negative ratings on a recent job evaluation, according to the Times. That prompted A.J. Duffy, president of United Teachers Los Angeles, to complain that teachers will be fired who, with some assistance and mentoring, could have become excellent teachers.

He’s right, which is all the more reason that California should extend its probationary period from two years to at least three. That way, struggling but committed teachers could have another year to get better.

Most states now have probationary periods of three or more years. California’s two-year period and its scant evaluation process are reasons why the National Council on Teacher Quality gave the state a D- rating – along with many other states – in identifying effective teachers.

Five years ago, Schwarzenegger backed an initiative that would have extended teacher probation to five years. (He would have been smarter to go for three or four.) The California Teachers Association poured in money to help defeat it at the polls, and the issue hasn’t been raised seriously since.