Long Island principal Carol Burris recently examined the effects of Michelle Rhee’s IMPACT program in DC.

It was started in 2009. By now they have enough data to identify all the great teachers, right?

They know enough to demonstrate whether three great teachers in a row closes the achievement gap, right?

But test scores in D.C. have been nearly flat since IMPACT was adopted.

The achievement gap in D.C.–for both blacks and whites, Hispanics and whites–remains the largest of any urban district tested by the National Assessment of Educational Progress.

So what happens to Rhee’s favorite tale about three great teachers in a row?

Apparently IMPACT has neither identified them nor found enough to make a difference.

Instead, the teacher attrition rate has increased.

By now, only “great” teachers should be left standing.

But obviously it doesn’t work that way.