The District on Friday fired 206 teachers for poor performance, a rarity in a big city school system and an extension of former chancellor Michelle A. Rhee’s aggressive drive to upgrade classroom instruction in the nation’s capital.

The teachers who were dismissed — about 5 percent of 4,100 who work for the school system — received low scores in the evaluation program known as IMPACT, developed under Rhee before she resigned in October.

Although policymakers at all levels of government are putting more emphasis on teacher quality, such large-scale dismissals remain all but unheard of. Collective-bargaining agreements with politically potent unions and cumbersome appeals processes often limit a school chief’s power to fire teachers.

Friday’s dismissals remove any lingering uncertainty that Mayor Vincent C. Gray (D) and Chancellor Kaya Henderson would continue personnel policies Rhee left behind. Gray received heavy support from organized labor in his campaign to unseat former Mayor Adrian M. Fenty (D), Rhee’s boss.

“We must embrace IMPACT as one of the tools that will allow us to achieve true education reform for the District’s school system,” said D.C. Council Chairman Kwame R. Brown (D).

IMPACT grades teachers on five 30-minute classroom observations and their compliance with nine broad standards. These include the abilities to express course content clearly, teach students with differing skill levels and manage time effectively. For some teachers, half of their appraisal is contingent on whether students meet predicted improvement targets on standardized tests.

Of the 206 fired, D.C. officials said, 65 were rated ineffective this year and 141 were judged minimally effective for the second consecutive year, triggering dismissal. That represents almost three times the 75 fired for poor performance when the first IMPACT ratings were calculated last year. Four teachers who received ratings of minimally effective for a second year were granted exceptions by Henderson, enabling them to stay in their positions at the request of principals, who said they showed potential for improvement.

In all, 413 school system employees — including teachers without proper licensing and support workers outside the Washington Teachers’ Union bargaining unit — were let go Friday. Teachers can appeal their firings to Henderson and the city’s Office of Employee Appeals.

The city reported that 663 teachers (16 percent) were rated as highly effective under IMPACT, making them eligible for bonuses of up to $25,000. And 528 (about 13 percent) were deemed minimally effective, placing them at risk for dismissal next year.

The vast majority of teachers — 2,765 — were rated effective.

D.C. public schools and other school systems have had annual evaluation systems for many years. But they have typically been pro forma affairs, with the overwhelming majority of educators receiving satisfactory ratings.

Rhee, citing research that showed that teacher quality is the largest in-school factor driving test-score growth, revamped evaluations. Her effort was buoyed by an unusual provision of D.C. law that exempts evaluation systems from collective bargaining. In many other cities, evaluation systems are subject to negotiations. That meant Rhee enjoyed broad latitude in designing IMPACT. The result — two straight years of significant teacher firings — has drawn wide notice.

“IMPACT is allowing us to do exactly what we set out to do,” Kaya Henderson, pictured in June, said. (Marvin Joseph/WASHINGTON POST)

“The only people who typically lose their jobs in districts are people who are guilty of a crime,” said Kate Walsh, president of the National Council on Teacher Quality, which promotes improved instruction in schools. “It’s rare that there are any significant numbers of teachers who lose their jobs because they are not good at teaching their subjects.”

Henderson expressed satisfaction with the personnel developments. Although the number of top-rated teachers remained unchanged from 2010, she said she was pleased that nearly 60 percent of the 566 teachers judged minimally effective last year moved up to effective or highly effective. She credited improved coaching and professional development for the shift.

“IMPACT is allowing us to do exactly what we set out to do,” Henderson said. “It rewards our high performers, helps us develop those who are struggling and moves out low performers.”

WTU President Nathan Saunders challenged her assessment.

“I agree that IMPACT is working exactly the way it was designed, and there are some flaws in the design,” he said. IMPACT puts teachers who work in challenging, high-poverty schools at a disadvantage, making it difficult for them to get high scores, he added.

A breakdown by ward confirms, as it did last year, that the overwhelming majority of highly effective teachers work in schools with lower rates of poverty and other social problems. Figures show that 135 of the 663 top-rated instructors (21 percent) are in Northwest Washington’s Ward 3. Wards 7 and 8, east of the Anacostia River and far less affluent, have a total of 71 educators ranked as highly effective.

Saunders said such figures confirm an inherent bias in the evaluations.

The school system “suffers from the belief that those who teach in Ward 7 or 8 are not good teachers,” he said, adding that teachers in those schools need more help.

Henderson agreed that teachers would benefit from more support and that high-poverty schools need to become more attractive places for high-performing teachers to work, with better leadership and safer environments.

But she rejected suggestions that top teachers should be reassigned to more-challenging schools against their wishes or that IMPACT rules should be softened.

“I won’t lower standards for teachers teaching in difficult situations,” she said. “It’s not fair to kids.”