D.C. school officials said Wednesday that 98 teachers were fired this week for poor performance, a large-scale dismissal that has become almost routine in the city but remains rare among school systems nationwide.

Those who were dismissed — about half the number let go last year — account for less than 3 percent of the school system’s approximately 4,100 teachers.

They received low scores on the rigorous evaluation instrument known as IMPACT, which has drawn national attention as one of the first to link teacher pay and job security with classroom performance and student achievement.

That concept has gained traction among policymakers around the country, said Sandi Jacobs of the National Council on Teacher Quality, a Washington-based advocacy group.

But the D.C. Public Schools system, which has dismissed nearly 400 teachers since 2009 because of poor performance, is still one of the few in which an unsatisfactory rating can lead to a rapid exit.

“Most of the new next-generation evaluation systems haven’t really hit the ground yet,” Jacobs said. “Nobody’s where DCPS is.”

This week’s firings are the second round of teacher dismissals under Mayor Vincent C. Gray (D), who received considerable support from the local teachers union during his 2010 campaign.

The numbers released Wednesday include only teachers in traditional public schools. Public charter schools have latitude to use their own evaluations.

Under IMPACT, teachers are observed five times each year. They’re graded on their ability to meet nine standards, including managing time, explaining information clearly and correcting students’ misunderstandings.

For some teachers — those who teach math or reading in grades four through eight — half their evaluation depends on how students fare on yearly standardized tests.

Of the teachers dismissed this week, 39 were rated ineffective on IMPACT, and 59 were rated minimally effective for the second year in a row.

“We owe it to our teachers to provide them with more and better curricular resources and professional development to ensure their success — and we’re doing that,” Schools Chancellor Kaya Henderson said in a statement. “But we owe it to our students and families to continue to move out the professionals who are not up to this incredibly difficult task.”

About two-thirds of all teachers were rated effective.

Teachers rated highly effective are eligible for bonuses of up to $25,000. This year, 988 teachers — or about a quarter of the teaching corps — earned that top rating, up from 663 last year.

The bonuses are expected to cost about $8 million this year, funded by outside donors, said schools spokeswoman Melissa Salmanowitz.

Starting next year, the school system will absorb the cost, budgeted for about $6 million.

IMPACT, first implemented in 2009 by then-Chancellor Michelle A. Rhee, has drawn fire from union leaders and many teachers, who consider it rigid, punitive and overly dependent on test scores.

Washington Teachers’ Union President Nathan Saunders, one of the fiercest critics, said the evaluation system is flawed but has been improved through recent revisions. If a teacher with promise appears headed for a poor IMPACT rating, for example, a principal can now ask to waive the consequences and give the teacher another year to improve.

“It’s been softened up. It’s become more collaborative than when it was first introduced,” Saunders said.

School officials anticipate announcing another round of IMPACT revisions soon. Saunders said he is hopeful that student test performance will no longer account for half a teacher’s evaluation score.

Union leaders would also like teachers to be able to appeal IMPACT scores through arbitration, a right that they are seeking to win in a pending court case.

Saunders also said he thinks that teachers are generally faring better on IMPACT because they’ve become accustomed to it. The union has made a concerted effort to help teachers navigate the system, coaching about 800 members in IMPACT courses over the past two years.

Gray has largely continued education reforms begun by his predecessor, Adrian M. Fenty (D). But the mayor has voiced concern that IMPACT is unfair to teachers working in the city’s poorest neighborhoods, where many children come to school with intensive needs. A ward-by-ward analysis of this week’s firings was not yet available.

Besides teachers let go for ineffectiveness, 95 were dismissed for licensure problems. And 51 teachers were terminated because their positions were eliminated in 2011 for budgetary or other reasons and they failed to find another permanent job.

In addition, 53 school employees who aren’t represented by the teachers union, such as custodians and clerical staff, were fired for poor performance.