D.C. schools officials have made their most significant modification yet to the IMPACT teacher evaluation system, one that allows educators who score consistently in the highly-effective range to skip the final three of their five annual classroom observations.

The change, first reported today by the Washington Examiner, involves teachers who have received “highly effective” ratings for the past two school years. If they achieve the same ratings on their first two evaluations this fall, they can opt out of the other three. There are 290 teachers (out of 4,100 total) who would be eligible if they aced their first two observations this year.

The move appears to be a recognition that principals and master educators — expert teachers independent of any school — have better uses for their time than five annual visits to the classrooms of consistently excellent instructors. A rough calculation shows that the opt-out provision, which will be tried on a pilot basis this year, could free up more than 400 observation hours for other things — such as helping lower-performing teachers raise their games.

DCPS has tweaked IMPACT here and there since it was introduced in fall 2009 by then-Chancellor Michelle A. Rhee. Earlier this summer, school system human capital chief Jason Kamras told principals that if they saw promising young teachers headed for a second consecutive “minimally effective” rating — which triggers dismissal — they could ask for a waiver. After union protests, the waiver rule was expanded to cover any teacher who principals believed was capable of improvement.