The District is changing the rules governing its teacher evaluations, encouraging public schools to reduce the emphasis on standardized test scores when rating their teachers.

The Office of the State Superintendent of Education announced Wednesday that D.C. Public Schools and certain charter schools no longer have to base 50 percent of teachers' evaluations on the results of the DC Comprehensive Assessment System, or DC CAS.

Instead, the standardized tests can count toward 30 percent of the evaluation, or any variation in between 30 and 50. The gap should be filled with other performance measures such as SAT scores, literacy assessments or end-of-course exams, OSSE officials said.

"The time has arrived for a holistic measure of teacher evaluation," said State Superintendent Hosanna Mahaley.

D.C. Public Schools and the 29 charter school operators regulated by the federal Race to the Top grant program must seek approval from OSSE to make the changes.

Frederick Lewis, a spokesman for D.C. Public Schools, said the school system is "considering" applying.

The Washington Examiner first reported in April that DCPS was considering scaling back the weight of evaluation tool Impact for teachers in tested classrooms.

Impact is one of the most controversial reforms of former Chancellor Michelle Rhee because poor ratings have led to the firings of hundreds of teachers -- 206 last summer alone. Classroom observations and whole-school performance also factor into the evaluations.

Because the District receives grant money from its successful Race to the Top application, it has had to stick with the reforms it outlined until the U.S. Department of Education approved the modification announced Tuesday.

Robin Chait, director of teaching and learning at OSSE, said a task force has been working on the changes. "It's something we've been talking about as the charter schools are implementing more rigorous evaluation systems for the first time this year, and DCPS has had Impact for a couple years now," Chait said.

Mahaley said multiple performance measures would allow teachers to provide midyear interventions if student data show help is needed; teachers don't receive DC CAS results until the summer.

Washington Teachers' Union President Nathan Saunders, who has been critical of Impact and other reforms instituted by Rhee, said he believes weakening the test's role in evaluations is a move in the right direction.

"The scores don't reflect the existing conditions that students bring into the classrooms, issues pertaining to family dysfunction, economic circumstance, poverty," Saunders said. "There are [problems] that are more immediate that young people face in their neighborhoods and communities, that if they face those on the day of testing could totally devastate their scores and their teacher's career."