How much value add do you need to lift performance?

Building off the Fordham Foundations analysis of the 2012-13 school report card data, and interesting question arises. Two of the measures receiving letter grades are the Performance Index and Value-add. Here's how Fordham describes the two

The performance index (PI) rating is a gauge of student achievement within a school or district. The performance index is a scale from 0 to 120, and schools or districts earn more points when students achieve at higher performance levels on Ohio’s standardized exams.
The second key indicator of school performance is its overall value-added rating, a measure of a school or district’s contribution to or impact on student learning progress. While the performance index takes a snapshot of student achievement—a one-year look—value-added takes a multi-year view of achievement. Value-added forecasts the achievement level that a student should reach by the end of the year, relative to her peers, and is determined by her previous years’ test scores (as many as available, starting with 3rd grade). Then on the basis of her actual performance that year, it determines whether she falls short, meets, or exceeds the projected achievement level.
Both approaches to viewing a school’s performance have pros and cons. Zeroing in on achievement alone risks mislabeling a school as failing academically, when it may be doing a great job helping students make big gains after starting out far behind. At the same time, focusing only on student progress, while ignoring achievement, may conceal the fact that students, even those making solid gains, remain far below the academic standard necessary to enter college or to obtain gainful employment upon graduating from high school. After all, we don’t just want students to make progress every year; we also want them to be “college and career ready” by the end of their K-12 experience.

That seems reasonable on its face. Here's what Fordham found in some instances

The picture blurs, however, when schools have mixed ratings. A small slice from the 2012-13 report card data in Dayton illustrates the problem.

School Building Public School Type Performance Index (Achievement) Rating Value-Added (Progress) Rating % Economically Disadvantaged
Kemp PreK-8 School District D A >95.0
World of Wonder PreK-8 Schoo District D A >95.0
Klepinger Community School Charter D A >95.0
Horizon Science Academy Dayton Charter D A >95.0
Dayton Leadership Academies- Liberty Charter D A >95.0

These schools, according to the data, are producing very healthy learning gains within distressed student populations, but are still unable to promote these students in to a successful academic career. Just how much extra learning, and for how long does a school need to provide A rated value add in order to lift achievement from a D to an A?

Here's the Fordham report

Parsing Performance Analysis of Ohio's New School Report Cards