A just-released report by DC Action for Children verifies what The Washington Examiner predicted two years ago. Impact -- former DC Public Schools Chancellor Michelle Rhee's much-heralded new approach to transforming one of the nation's worst public schools systems -- hasn't had much of an impact.

According to the group's independent analysis of D.C. standardized test scores, third-graders who spent their entire academic lives under Impact made only statistically insignificant gains in math and reading since 2007, when the School Reform Act was passed and Rhee began implementing her reforms.

Rhee established two career tracks: a "Red Track" for teachers who wanted to retain tenure with smaller pay increases and no bonuses, and a "Green Track" for those who relinquished tenure in return for higher pay and performance bonuses. But the contract Rhee negotiated with the Washington Teachers' Union gave all teachers a 21.6 percent raise over five years, pushing their average salary to $74,400, in addition to thousands more in medical, dental, legal and retirement benefits, tuition assistance, travel and cellphone reimbursement and certification bonuses.

This is why DCPS spends more per student than virtually any other school district in America. But the initial promise that Impact would lead to higher test scores has not been realized. Although Rhee was able to fire hundreds of teachers rated "minimally effective" under Impact's complicated evaluation system, hundreds more received pay raises before they had actually earned them.

"We are spending way too much effort and money in education reform not to see results," DC Action for Children Executive Director HyeSook Chung acknowledged. That's because the flaw in Rhee's approach was to hand out raises before they were justified by higher student achievement.

Financial incentives can be useful tools to change behavior, but not when people are rewarded before they've produced the desired results. This is precisely what happened at DCPS. Teachers are still cashing larger paychecks, even though third-grade proficiency -- a key indicator of high school graduation -- has remained stagnant. In other words, Impact has had very little impact except to fatten union members' bank accounts.

It's poetic justice that Rhee's successor, Kaya Henderson -- who was Rhee's chief negotiator with the union on Impact -- has to figure out another way to get better results from what is now the highest paid public school teaching staff in the country.