For instance, it notes a 2006 letter from then schools CEO Arne Duncan, now U.S. secretary of education, stating that the share of CPS students meeting or exceeding state standards had leapt 15 points in one year.

  In fact, it says, the change occurred because of a change in the test, not because of real educational gains. As a result, it points out, while a test cited by local officials showed that 71% of 8th graders met or exceeded state standards in 2007, a national test taken here the same year showed just 13% were up to par.

  Similarly, while the test employed locally reported that the share of 8th graders meeting math standards grew from 32% to 71% from 2005 to 2007, the national test, sponsored by the U.S. Department of Education, showed scores effectively flat, moving from 11% to only 13%.