Most Los Angeles Unified School District teachers lock in their careers after only two years on the job, often with little oversight — something the superintendent is vowing to change.

“Too many ineffective teachers are falling into tenured positions — the equivalent of jobs for life,” Ramon Cortines told the Los Angeles Times.

Administrators are required to sit in on classes, for at least 30 minutes, at least once before a teacher is granted tenure, but some teachers told The Times that doesn’t always happen, and the evaluations that do take place are sometimes void of substance.

A Times survey showed that probationary teachers were assigned to schools in poor neighborhoods in higher numbers and less likely than their peers to be denied tenure.

In response, district administrators emphasized that at least 15 percent of teachers quit on their own after their first year, and that could have skewed the findings.

According to a 2008 survey done for the LAUSD by the nonprofit New Teachers Project, 44 percent of principals said they did not always remove probationary teachers they thought did not belong in the job.

Interviews by The Times suggest several explanations:

• Principals are afraid they’ll get someone worse.

• It is time-consuming to prepare and unpleasant to deliver a negative evaluation.

• They learned not to be picky during teacher shortages that ended years ago.

• Or they simply can’t tell who deserves a permanent job and who doesn’t.

Some officials also say principals have grown gunshy from taking on permanent teachers. They are rarely fired and even then, can spend years on the payroll as their cases wind through a long appeals process, The Times reported in May.

A 1983 law stripped probationary teachers of employment protections, so they could be dismissed without cause. In exchange, teachers unions persuaded legislators to reduce the probationary period from three years to two.

Most states require three, while some mandate as many as five, The Times reported.

In 2005, Gov. Arnold Schwarzenegger campaigned for Proposition 74, which would have extended the probationary period to five years, but it was defeated, thanks in no small part to the California Teachers Association and others spending nearly $17 million to oppose it.

Meanwhile, the Obama administration is making teacher accountability a key requirement in the competition for $4.35 billion in education grants.

The mayor’s Partnership for Los Angeles Schools, which controls some of the district’s lowest performing campuses, is requiring principals to spend three hours a day in classrooms at Samuel Gompers Middle School in South Los Angeles.

Sonia Miller described trying to document the numerous shortcomings of a teacher who was frequently absent.

She told The Times she has been documenting the teacher’s failings almost every day for more than a year.

“I’m told it will take another year of writing to get [the teacher] out,” she told the newspaper.

Instead of being fired, she said, the tenured instructor will almost certainly land on another L.A. Unified campus.

Cortines last week said he wants ineffective new teachers weeded out, saying the nation’s second-largest school system has largely failed to adequately evaluate teacher performance.

“This district can be rightly criticized for the promotion of ineffective teachers over the years. That is about to change,” Cortines told The Times. “We do not owe poor performers a job.”

Taking aim at weak probationary teachers now could spare the district from firing others who are more effective but have slightly less experience next summer, when there will probably be another round of layoffs. Teachers must be let go by seniority, according to state law, which has forced the district to ignore performance in its dismissals, officials told The Times.

Cortines’ statement came a week after The Times presented L.A. Unified with the results of an investigation that found the district often does not meaningfully assess new teachers before they are granted tenure.

Cortines urged district officials to scrutinize the 404 probationary teachers who received a “needs improvement” on one or more criteria on their evaluations last year, The Times reported.

The superintendent also urged greater monitoring of 339 administrators who have not yet become permanent and 175 tenured teachers and other employees who received negative evaluations last year, according to The Times.

“The days of coddling ineffective teachers, or allowing them to be moved to another school, are over,” he told the newspaper. “No more excuses.”