do assunto da notícia anterior [coincidências...!]... não é por acaso que os resultados das charter schools andam a ser postos em causa... lá pelos 'states'...!

"There have now been several stories in the New York news media about New York City’s charter schools’ “gains” on this year’s state tests (see here, here, here, here and here). All of them trumpeted the 3-7 percentage point increase in proficiency among the city’s charter students, compared with the 2-3 point increase among their counterparts in regular public schools. The consensus: Charters performed fantastically well this year.

In fact, the NY Daily News asserted that the “clear lesson” from the data is that “public school administrators must gain the flexibility enjoyed by charter leaders,” and “adopt [their] single-minded focus on achievement.” For his part, Mayor Michael Bloomberg claimed that the scores are evidence that the city should expand its charter sector.

All of this reflects a fundamental misunderstanding of how to interpret testing data, one that is frankly a little frightening to find among experienced reporters and elected officials.

As I’ve discussed many times, short-term changes in raw state testing results (whether scores or rates), especially small changes, are almost always a poor gauge of schools’ effectiveness. This is true for several reasons, one of them being that you’re comparing two different groups of students (i.e., the data don’t follow students over time).

In the case of charter schools, this is an even more critical consideration, as charter sectors tend to be relatively small and in rapid flux. It seems that almost nobody thought to check on this before drawing conclusions from this year’s NYC’s charter schools’ results.

Had they done so, they would have found that charter enrollment increased a rather incredible 25 percent between 2010-11 and 2011-12, to roughly 47,000 students (most of this jump is presumably due to 11 new schools opening). This means that almost 10,000 of these students, a large proportion of them in tested grades, were not in charters last year.

There is no way to know, based on the public data, how this affected the results."

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