More students are taking Advanced Placement tests, but the proportion of tests receiving what is deemed a passing score has dipped, and the mean score is down for the fourth year in a row. Data released here this week by the New York City-based nonprofit organization that owns the AP brand shows that a greater-than-ever proportion of students overall--more than 15 percent of the public high school class of 2007--scored at least one 3 on an AP test. The tests are graded on a scale of 1 to 5, the highest score. Yet, as the number of AP exams taken in U.S. public schools has ballooned by almost 25 percent over the four years that the College Board has released its "AP Report to the Nation," the percentage of exams that received at least a 3--the minimum score that the College Board considers predictive of success in college--has slipped from about 60 percent to 57 percent. The mean score on the nearly 2 million AP exams taken by students in last year's U.S. public graduating class was 2.83, down from 2.9 in 2004. Ms. Jennifer Topiel, a spokeswoman for the College Board, said the score declines are a major concern for the organization, as are widening score gaps between some racial and ethnic groups, "particularly those among underrepresented students who are not being prepared and not having the same resources."