Great Performance !

Aside from its longevity, there are several reasons the CPS school-choice program is a good one to study. It offers a huge data set— Chicago has the third-largest school system in the country, after New York and Los Angeles—as well as an enormous amount of choice (more than sixty high schools) and flexibility. Its take-up rates are accordingly very high, with roughly half of the CPS students opting out of their neighborhood school. But the most serendipitous aspect of the CPS program—for the sake of a study, at least—is how the school-choice game was played.

As might be expected, throwing open the doors of any school to every freshman in Chicago threatened to create bedlam. The schools with good test scores and high graduation rates would be rabidly oversubscribed, making it impossible to satisfy every student’s request.

In the interest of fairness, the CPS resorted to a lottery. For a researcher, this is a remarkable boon. A behavioral scientist could hardly design a better experiment in his laboratory. Just as the scientist might randomly assign one mouse to a treatment group and another to a control group, the Chicago school board effectively did the same. Imagine two students, statistically identical, each of whom wants to attend a new, better school. Thanks to how the ball bounces in the hopper, one goes to the new school and the other stays behind. Now imagine multiplying those students by the thousands. The result is a natural experiment on a grand scale. This was hardly the goal in the mind of the Chicago school officials who conceived the lottery. But when viewed in this way, the lottery offers a wonderful means of measuring just how much school choice—or, really, a better school— truly matters.

So what do the data reveal?

The answer will not be heartening to obsessive parents: in this case, school choice barely mattered at all. It is true that the Chicago students who entered the school-choice lottery were more likely to graduate than the students who didn’t—which seems to suggest that school choice does make a difference. But that’s an illusion. The proof is in this comparison: the students who won the lottery and went to a “better” school did no better than equivalent students who lost the lottery and were left behind. That is, a student who opted out of his neighborhood school was more likely to graduate whether or not he actually won the opportunity to go to a new school. What appears to be an advantage gained by going to a new school isn’t connected to the new school at all. What this means is that the students—and parents—who choose to opt out tend to be smarter and more academically motivated to begin with. But statistically, they gained no academic benefit by changing schools.

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Taken From : FREAKONOMICS - A Rogue Economist Explores the Hidden Side of Everything