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.