Quoting from a New Haven Register story as repeated in the article:

Last year, 19 of the 56 students in Amistad's ninth grade—the same cohort that scored so well on the eighth-grade tests in 2007—failed at least one course. And 11 students, 20 percent of the grade, failed two courses, meaning that they did not move on to the tenth grade.

Quoting the author's summary:

It's not quite clear just what this means. Last year, the 10th-grade students at Amistad once again did very well on the state achievement tests. So by outside measures, achievement at the school remains high. And yet many students are struggling to meet Amistad High's own standards, even after four or five years of Amistad education.

[End quotes]

So students do well on tests and fail subsequent course work. A quote fropm the school considers independent thought an important issue. The author blames past experience from before the charter school.

I think the school itself was trying to give the simplest explanation a quasi-positive spin. The students were intensively taught the test. Limited rote learning. They go beyond what they're taught, they fail.

Standardized tests are necessary. So is learning the basics. But successfully teaching to the test shouldn't lead to over-optimistic preedictions of future learning, I suspect.