Both the mayor and the chancellor have now issued statements boasting about gains on Advanced Placement exams, the rigorous tests that are considered a good indicator of whether students are prepared for college. But the picture is more complex than they suggest, and if anything the evidence adds to concerns raised yesterday about college preparedness, particularly among black and Hispanic students.

More students are definitely taking the exams than were in 2002, whether you look at the sheer numbers — a total of 23,600 students took the tests in 2008, up from less than 17,000 in 2002 — or at proportions — in 2008, about 23% of eleventh- and twelfth-graders took AP exams, up from 21% in 2002.*

But, as I suggested yesterday, the increased participation has led to a lower pass rate:

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A falling pass rate is not necessarily bad. If more students are taking exams, it’s likely that some of those new additions would have done worse in past years, too — they just didn’t take the exams in past years. But remember that students are not joining the AP pool at random. Those who take AP exams are usually students who are already enrolled in rigorous classes. If adding a group of relatively high-level students to the pool pushes the AP pass rate down, that’s not too promising. And I’m not even getting into the fact that “passing” is defined as getting a 3, 4, or a 5 on a 1-to-5 scale‚ when some colleges only accept a 4 or 5 score as actually passing.

Black and Hispanic students appear to struggle most on the exams. More students took the exams from every racial group last year, but only black and Hispanic students’ pass rates declined:

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Meanwhile, though it’s impossible to calculate the exact percentage of students that took AP exams, a rough estimate* suggests that participation rates are still very low. Only 12% of black eleventh- and twelfth-graders and only 16% of Hispanics took at least one of the exams in 2008, by the rough estimate, up from 9% and 14% respectively in 2002.

Not everyone has to take AP exams, to be sure, and many city high schools do not even offer the high-level classes that prepare for the exams. But doing well on them is a good predictor of success in college, and students who want to apply to competitive colleges often do take them.

*The best way to measure the proportion of students who took AP exams would be to divide apples into apples: For instance, to divide the number of 12th-graders taking an exam into the total number of twelfth graders. A Department of Education spokesman, Andrew Jacob, told me that these figures aren’t available this year. The College Board did not break down New York City test-takers by grade level. Therefore, to calculate proportions, I had to assume that the test-takers were eleventh- and twelfth-graders, and I divided that number into the total number of eleventh- and twelfth-graders in the city.