The decades-old tradition of tenure protects teachers, often frustrates principals and has even surfaced as an issue in the presidential campaign. Now tenure itself is under review.

Tenure guarantees that public school teachers who have this protection cannot be fired without legitimate cause and due process, perhaps even a court hearing. Almost every state provides tenure in some form.

Yet with federal law requiring schools to have a top teacher for every core class, more administrators are questioning whether tenure keeps them from getting rid of instructors who just are not good enough in the classroom.

Sen. John F. Kerry (D-Mass.), the presidential candidate favored by education unions, wants to make it easier for schools to act quickly against poor teachers, provided that educators are protected from baseless firings.

To teachers, tenure is a coveted and often misunderstood right -- not a lock on a lifetime job, but assurance of fair treatment, including intervention for teachers who may be struggling to reach students.

"It's protection against the false accusations, against politically trumped-up charges, against people who insist you must teach a certain way or risk getting fired," said Penny Kotterman, a special-education teacher and president of the Arizona affiliate of the National Education Association. She spoke during a group interview last week at the NEA's annual meeting.

Tenure is most associated with colleges and universities, where prospective professors earn it by compiling a rigorous record of research, teaching and service.

In the kindergarten through high school world, it is typically granted to teachers after two to five years of solid performance in a district, although debate continues over its value as a sign of quality.

Most principals and superintendents say tenure does not mean teachers have proved themselves to be very good, and many teachers agreed with that point in polls by the nonpartisan Public Agenda research group.

But Kotterman said that is off the mark. Tenure, she said, is meant mainly as an assurance of fair review, while certification and regular evaluation of teachers are indicators of quality.

In the polls, most teachers said tenure protects them from district politics and losing their jobs to newcomers who could be hired for less.

David Sanchez, a kindergarten teacher from Burlingame, Calif., said tenure has helped teachers who were being pushed out of jobs in retaliation for union activity.

Charles Hasse, a fourth-grade teacher and president of the Washington Education Association, said tenure helps because schools have fewer people in supervisory roles than many employers do, making "the opportunity for misjudgments much greater."

School administrators, who are often former teachers, say they understand the point of tenure. But they say it can lead to frustrating delays in replacing poor teachers, leading some administrators to give up trying.

In Oklahoma, trying to remove a tenured teacher can lead to a court hearing, said Ruth Ann Carr, superintendent of Ardmore City Schools. "You have to have people who are willing to go the distance on those type of employment situations," Carr said. "They end up feeling like they're the ones on trial."

Teachers union leaders say they support expedited reviews, but they take issue with the argument that tenure protects poor teachers. They say administrators should have no problem making a clear case against those who cannot or will not improve.

States offer legitimate reasons for firing tenured teachers, from immorality to insubordination; not all directly address teaching performance.

The challenge, critics say, is getting rid of mediocre teachers, not the ones who commit egregious conduct violations.

Yet Michael Kramer, who represents teachers as general counsel for the Georgia Association of Educators, says tenure can help the educational mission by protecting strong, outspoken teachers.

"It's the brightest, the risk-taking teachers," he said, "who are most at risk for arbitrary dismissal."