I talked for a bit last night with a DCPS teacher about IMPACT. While he expressed some concern about the system, he also said he was proof of it's effectiveness. See, he's a third-year elementary teacher at a struggling school in Northeast. He had twenty kids on IEPs in his class last year--which, along with the extra strife that caused in the classroom, meant hours of added administrative work. This spring, he got a job offer to teach at a school in a wealthy Virginia district--with a guarantee of no more than five IEP students per year and a significant salary bump.
He didn't take the deal. Why? Because he was ranked highly effective this past year and earned himself a $15,000 bonus through IMPACT. That bonus was enough to keep this quality new teacher in a classroom at a needy DCPS school. (A big deal when you note that the trajectory of so many strong teachers is to "put in their time" at an urban school and then slide over to a cushy job in a suburban district, draining our cities of teacher talent.)
So on that front, IMPACT seems to be working.