KIPP gains survive new scrutiny, with a footnote

Jay Matthews:

New research on the nation’s largest and best-performing charter school network has a dull title — “Student Selection, Attrition, and Replacement in KIPP Middle Schools” — but it adds fuel to a fierce national debate over why KIPP looks so good and whether schools should follow its example.
No charter school network has been researched as much as KIPP, which has 125 schools and 39,000 students in 20 states and the District. Most of the studies say its schools have had large and positive impacts on student achievement when compared to regular public schools. But some smart critics, including scholars Richard Kahlenberg of the Century Foundation and Gary Miron of Western Michigan University, have found a potential glitch in the analysis.
Most KIPP campuses are fifth-through-eighth-grade middle schools. Students arrive far below grade level but flourish because of KIPP’s longer school days and years and careful teacher selection, training and support.
Nonetheless, some KIPP parents move away or decide KIPP is not right for their children. Kahlenberg and Miron say that inflates the average scores of students who stay, compared to regular schools: At KIPP schools, they argue, lower-performing students who leave early are not replaced by incoming low scorers as they are in regular schools.