The Prince George’s County’s school system has quietly but steadily increased the number of teacher firings in recent years, as officials push for tougher performance standards.

In the school year that just ended, data show, 89 teachers were terminated for “incompetence,” based on two straight years of “unsatisfactory” ratings on performance reviews. In 2007-08, the number fired for incompetence was 25.

The increase reflects a new emphasis on measuring teacher performance in the county, mirroring a national trend that has concerned some union leaders.

“Before, I think there was a push to land every teacher at satisfactory,” said county schools Superintendent William R. Hite Jr. “It used to be held that a teaching job is forever. That being a principal is a job forever. All of that is beginning to change. You have to be effective.”

Since Hite took the helm of the school district in December 2008, the number of teacher firings has been on the rise — doubling in his first year and increasing every year since.

Over the past five years, Maryland’s second-largest school system has terminated 299 teachers rated incompetent. The scale of those terminations is on par with actions in Montgomery County, the largest system, where 135 “certificated employees” — including teachers and school psychologists — were recommended for dismissal in the same period. An additional 240 resigned or retired before completing a process known in Montgomery as peer assistance and review.

In Prince George’s, Hite said, about a dozen principals had been removed or demoted for incompetence over the past two years, which he called “gigantic.”

Such statistics echo headline-making firings in the District in recent years. When she was D.C. schools chancellor, Michelle A. Rhee drew fierce union criticism after creating an evaluation system known as IMPACT that tied performance evaluations to test scores.

IMPACT, still in use under Rhee’s successor, Kaya Henderson, led to 206 teacher firings this year in a school system less than two-thirds the size of Prince George’s.

By comparison, Hite’s terminations are minuscule. They amount to barely 1 percent of the county’s 9,000 teachers. So far, Hite has not faced any significant union backlash.

Hite said he does not think the system can improve simply by firing bad teachers. But he said he shares Rhee’s view that critical evaluations not only can identify bad teachers, but also help develop promising employees and yield better classroom results.

Unlike IMPACT, the Prince George’s evaluations do not factor in student performance — that will change soon.

Currently, teachers are judged in four broad categories: planning and preparation, classroom environment, quality of instruction, and maintenance of professional responsibilities, such as keeping good records and punctuality. Poor performance in any of these leads to an unsatisfactory evaluation. Two unsatisfactory evaluations trigger dismissal.

Hite inherited that system. What changed, he said, is an increase in the number of teacher observations — to as many as four a year — and a willingness to deem a teacher incompetent.

“Not all teachers are bad,” Hite said. “This is about facilitating feedback and encouraging growth and development. Do some people have skills that need to be developed? Yes. Do some people need to be separated because they’re not effective teachers? Yes.”

The results, Hite said, are measurable. He mentioned the county’s significant gains in reading on the Maryland School Assessments. The number of elementary students scoring at proficient or better went up from 79 percent in 2010 to 82 percent this year.

The movement toward more critical evaluations has grown since the 2002 No Child Left Behind law required more highly qualified teachers in the classroom. Still, there is debate over how to determine objectively just how effective a teacher can be.

Kenneth Haines, president of the Prince George’s County Educators’ Association, said the “current evaluation method may not really be a valid indicator of teacher competency.”

“The checklist approach to teacher evaluation — where even one missed item can lead to an unsatisfactory evaluation — often leads to an increase in terminations for cause,” he said.

Haines said he supports appropriate attempts at mediation for those who are dismissed. Still, he said, “it does not strengthen the teaching profession or best serve children to keep poorly performing teachers.”

Prince George’s officials plan to revamp evaluations as part of a Maryland initiative funded by a federal Race to the Top grant.

The new evaluation tool, which Hite anticipates will be finalized in the coming school year, will factor in student test scores for the first time.

Organizations such as the Bill and Melinda Gates Foundation have poured millions of dollars into school districts with the aim of improving teacher evaluations. Prince George’s recently won a $2.5 million grant from the foundation to help the county schools create such a system.