This is the VOA Special English Education Report.

Students in Washington, DC, will return to classrooms this month to begin a new school year. But at least five percent of their teachers will not return with them. Last month, the District of Columbia public schools told 206 teachers that they are not good enough to stay.

The school system dismissed 75 teachers last year. It was the first year of a new teacher rating system.

Experts say such large numbers of dismissals are rare in American schools. But in Washington the rating system is not governed by the labor contract with the teachers union. So school officials have more freedom.

The system is called IMPACT. Teachers are observed in the classroom five times a year for at least 30 minutes each time. They are also judged by student test scores.

Administrators rated 65 of the 206 teachers as "ineffective." The others lost their jobs because they were rated "minimally effective" for a second year.

The National Council on Teacher Quality is a research group that works to increase the number of effective teachers. Emily Cohen, a policy director there, says the council supports the IMPACT system.

EMILY COHEN: "This is an evaluation instrument that is finally able to capture who is highly effective and who is ineffective and who could be doing better and could use some assistance. Most evaluation instruments in the country do not capture teacher performance -- all teachers are rated satisfactory."

Some Washington teachers say their ratings depend too heavily on test scores. For some teachers, half of their rating is based on how well their students do. But Emily Cohen says test scores are important.

EMILY COHEN: "Testing is probably one of the -- it's the most objective data that we have on teacher performance. The District also is looking at other things, using master educators to evaluate teachers. So it's not just looking at student test performance, it is using other sources of data."

Teachers with the highest rating -- "highly effective" -- can receive a performance bonus of up to 25,000 dollars. In addition, they can receive a pay increase.

Almost 60 percent of the teachers who were rated "minimally effective" last year stayed in the school system and improved. School officials say these teachers received help to become better.

Michelle Rhee created the IMPACT system. She gained national attention for her aggressive reform efforts when she led the troubled school system in the nation's capital. She left last year and her deputy, Kaya Henderson, took her place.

The Washington Teachers Union says IMPACT unfairly hurts teachers who work in schools with high rates of poverty. The Washington Post reported that most of the teachers with the highest rating work in schools with lower poverty rates.

And that's the VOA Special English Education Report. For more education news and to learn American English, go to voaspecialenglish.com. I'm Christopher Cruise.

dismissal: official notice that you have been fired from your job 解雇，免职

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（来源：VOA 编辑：实习生史莉萍）