> Hoxby is an enthusiastic partisan of charter schools. But her NBER
> paper I posted earlier claimed results of "0.09 standard deviations
> per year of treatment in math and 0.04 standard deviations per year in
> reading." I.e., rather tiny.
>
> http://www.nber.org/papers/w14852
Those numbers are per year and they accumulate; they are also in the same range of numbers that the CREDO study came up with (although it's with a sign-change). Anyway, I think you're misunderstanding the abstract of that paper. A better paper from Hoxby/NBER to look at is the one where they compare (in a different way from CREDO) those who go to charter schools and those who don't.
Which is, afterall, the topic at hand here ... no?
The 'different way' also makes more sense to me than the CREDO method, even after getting a much better explaination of it in their response[*]: they look at all the kids who *applied* to charter schools and then compare the ones who got in vs. the ones who didn't. They first establish that the lotteries are fair, which you'd want in this case, 'natch.
A key finding:
On average, a student who attended a charter school for all
of grades kindergarten through eight would close about 86
percent of the "Scarsdale-Harlem achievement gap" in math
and 66 percent of the achievement gap in English. A student
who attended fewer grades would improve by a commensurately
smaller amount. [Chapter IV]
[ So: more is better --JMH ]
On average, a lotteried-out student who stayed in the
traditional public schools for all of grades kindergarten
through eight would stay on grade level but would not close
the "Scarsdale-Harlem achievement gap" by much. However, the
lotteried-out students' performance does improve and is better
than the norm in the U.S. where, as a rule, disadvantaged
students fall further behind as they age. [Chapter IV]
[ So: wanting a change is better than not wanting it, even if you don't get it --JMH ]
It's interesting to note that NY State does not appear in the CREDO study; and NY State is known for having above-average oversight in the authorization mechanisms for charter schools.
I think another interesting finding is that there is above-average participation (both applicants and accepted children) by those who are black and those who are poor in charter schools in NYC; they are among the least-well-served in the traditional system.
Their parents are looking for a solution, and apparently finding it in charter schools.
/jordan
[*] After reading all about this dustup, I think your original point of putting the CREDO results out there as "Charter schools don't work" is (very) wrong: they clarify in the final retort that what they've found is that *some* charter schools have outsized negative performance, and they seem to be clustered in places that have less oversight; I wonder if anyone has correlated those results with the places where *corporate* charter schools have become popular . . . they also seem to acknowledge that the NYC results are different from what they found elsewhere. I do not believe it's accurate at all to say that CREDO supports your claim that "they don't work" ...