Freakonomics, baby:

The theory sounds great, but evidence confirming it has been hard to find. Julie Cullen and Brian Jacob, my good friends and co-authors, haven’t done school choice proponents any favors with their latest paper (the full version of which can be found here). Using kindergarten lottery outcomes that determine which kids get into the most sought-after schools, they are able to compare the outcomes of those who win the lottery versus those who lose. The students who win the lotteries go to “better” schools and have “better” peers, but they don’t have better outcomes. These results confirm the earlier findings that Julie, Brian, and I obtained when we examined the impact of lotteries on high school outcomes in Chicago.

Why don’t the kids who get access to “better” schools do better? That is a difficult question. Part of the answer is likely that the definition of “better” is based on outputs, like how high the test scores are at the school or what fraction of its students attend good colleges. That sort of metric ignores the fact that “better” schools tend to attract “better” kids. These are kids with strong families and good academic backgrounds. So even if the school is not at all good at adding value, it will still have the best outputs, because it had the best inputs. If the school does not have high value added, there is no reason to expect that a child who transfers there will do better than she did at her previous school. Parents don’t have good information on the inputs to a school, only the outputs, so it is difficult for them to accurately assess value added.