I’ve defended KIPP before from accusations that their performance is due to selection bias and cream skimming. A new paper from Josh Angrist and a bunch of other co-authors provides more evidence in KIPP’s favor. They found that KIPP benefited the weakest students and those with special needs most:

Our results show average reading score gains of about 0.12 standard deviations (hereafter, σ) for each year a student spends at KIPP, with significantly larger gains for special education and LEP students of about 0.3-0.4σ. Students attending KIPP gain an average of 0.35σ per year in math; these effects are slightly larger for LEP and special education students. We also produce separate estimates for students with different levels of baseline (4th grade) scores. The result suggests that effects are largest for those who start out behind their peers. Male and female students gain about equally in math, while boys benefit more than girls in reading. Finally, an examination of Massachusetts Comprehensive Assessment System (MCAS) performance categories (similar to quartiles) shows that  KIPP Lynn boosts achievement primarily by moving students up from the lowest group. Together,  therefore, the findings reported here suggest that KIPP Lynn benefits weak students the most.

The study also provides further evidence against the claim that KIPP’s model is based on kicking out the trouble students. The authors found that students who won the admissions lottery were no more likely to switch schools than those who lost, meaning that controlling for selection bias, KIPP students do not have a higher attrition rate.

Initial skepticism of KIPP’s high achievement results was understandable, and questions about cream skimming, kicking out bad students, and whether the weakest students were benefitting were important to ask. But the evidence continues to come in that KIPP is doing something right, and that skeptics were wrong about why that was. It’s time for skeptics to re-evaluate their positions. I’m hoping that when Diane Ravitch releases the “The Death and Life of the Great American School System” in paperback the section that is skeptical of KIPP is updated to reflect this new evidence.