Today's Education Gadfly and Wall Street Journal editorial both capture the most important news about Caroline Hoxby's well-publicized study on NYC charters ??? she rebuts the argument that charters' success rests on ???creaming??? the best students from district schools.

As the WSJ tells it:

The study nullifies any self-selection bias by comparing students who attend charters only with those who applied for admission through the lottery, but did not get in. "Lottery-based studies," notes Ms. Hoxby, "are scientific and more reliable."

In other words, she compares charter versus district school students without the worry that charter students are somehow different, not just demographically or academically, but because their parents may be more concerned about their educations (as evidenced by their choosing a charter). The comparison students/parents made that same choice, and they fared worse when left in a district school.

That's a pretty good rebuttal to charter critics like Richard Rothstein and Lawrence Mishel , who have argued (in part) that KIPP's success is over-stated because parents there are more motivated. (Rothstein has also argued that charters may not work well for kids whose parents are simply not motivated???Hoxby's analysis can't address that question.)

Yet Jonathan Gyurko (who certainly supports NYC charters) thoughtfully points out that it's not a perfect rebuttal. Hoxby herself suggests charters may indeed be getting better students (because the rejected students subsequently did relatively well in district schools, even if not as well as they would have in charters). Yet her bottom line remains: these charters are serving their students better than the district schools???regardless of the debate about where the students started.

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