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A statistician offers a caveat on single-school score celebrations

It’s not news to report that statistics can be deceptive. But when a new set of test scores come out, it’s worth repeating nonetheless.

Teachers College sociologist Aaron Pallas tackles the subject in the Community section of GothamSchools today, by taking a closer look at two middle schools that the Post has recently highlighted for exceptional performance and finding that both schools admit their students selectively. He writes:

Due to their selective admissions, IS 187 and, to a lesser extent, IS 364 were born on third base. The New York Post thinks they hit a triple.

Some schools might have hit something closer to a home run. Manhattan’s citywide Anderson School, for instance, admitted every single one of its students in grades 3-8 on the basis of their scores on an IQ test and in-person interview. Not a single student at Anderson failed the math test, and in fact it was the only school citywide with a clean 100 percent of all students in a single grade scoring at the very highest level, in the sixth grade.

Not all successful schools handpick their students. Another school the Post profiled, Carl C. Icahn Charter School in the Bronx, had just about every student in grades 3 through 8 pass the test. (Aaron didn’t include the school in his Post coverage criticism.) That school admits students by random lottery, in accordance with state law for charter schools. It does have a low proportion of students with special needs, just under 4 percent, according to data obtained by Insideschools.

Another school touting itself as a test-score success story, although it didn’t make the Post today, was Harlem Success Academy, the charter school operated by Eva Moskowitz. I got a press release from the school yesterday that said Harlem Success “slammed the 2009 New York State Math exam,” with 71 percent of students scoring at the highest level and 100 percent passing the test. The 71 percent figure made Harlem Success the top-performing charter school in the state and the 10th-highest school in the city overall, the release said.

But Harlem Success, actually a chain of four schools (so far), only had one set of kids taking the test this year, so the 71 percent figure is based on the scores of just 58 kids. In fact, 118 grades at 67 schools had higher proportions of students testing at the highest level than Harlem Success.