American public school principals are as nervous as 16-year-olds facing a semester final. More and more of them are being required to publish annual summaries of how they and their teachers are doing. The school report cards, as they are usually called, compare each school's test scores to state and national averages and provide data on everything from teacher qualifications to disciplinary mishaps.

In principle, this is not a bad idea. Everyone from the newest kindergarten parent to the president of the United States agrees that schools must be accountable. Unfortunately, the report cards, like other government mandates imposed on schools, often do more to distort than clarify what is happening in class.

This is particularly true of data on college-level courses and tests, such as Advanced Placement (AP) and International Baccalaureate (IB), which have become a vital part of high school curriculums. Many teachers are using the demanding courses and the independently written and scored tests to enliven the learning process for hitherto marginal students. But this effort fails to come across because of the clumsy way the states require that these courses and tests be assessed.

The report cards usually give the percentage of AP or IB tests that have received a passing score, a number high enough to entitle the student to college credit for the course. High school principals with pass rates of more than 80 percent brag about their success while those who fall below 60 percent cringe at the thought of a call from the superintendent.

When AP and IB were academic boutiques designed to save bright seniors at a few well-polished schools from boredom, this made sense. The very best of such schools' college-bound seniors should have been able to score the equivalent of at least a C. Anything less suggested inadequate teaching or too many keg parties in the woods behind the country club.

But in the past 15 years American educators have discovered that AP and IB provide a powerful way of engaging the interest not only of future Ivy Leaguers but of otherwise indifferent students, even some juniors and sophomores who in the past would never have been considered worthy of curricular high cuisine. More than half of all American high schools now offer AP courses and tests. The number of IB programs is much smaller, but growing rapidly, particularly in the Washington area.

Many students, considered unready or unwilling to learn, catch fire when exposed to a rigorous course designed to prepare them for a test over which their teacher has no control. Teachers use the daunting prospect of the test to motivate slackers and unify classes fractured by clique-ridden high school culture.

Teenagers like the idea of being graded not on the curve but on whether or not they meet a high national and international standard. Distracting competitive juices evaporate. Adolescents who come to school for no other reason than to see their friends find, to their pleased surprise, that they are rewarded for working together toward the common goal of acing the test.

What if they flunk the test and miss out on college credit? The teacher can still give a hard-working student a passing mark in her class, since her assessment is entirely separate from the grading of AP or IB tests. More important, students who have failed an AP or an IB test usually discover that they still know more about the subject and are better prepared for college than if they had never tried the course. They have gone one-on-one against the academic equivalent of Reggie Miller and lost, but they have a much clearer idea of what they need to get to that level.

Under the school report card system, however, their school suffers for letting them take that risk. A school such as Millburn High in affluent suburban New Jersey can brag about its 94 percent AP pass rate even as it bars dozens of eager and well-qualified students from taking AP courses and tests. A school such as Hayfield Secondary in Fairfax County can welcome students into its courses and see a heartening 14 percent increase in the number of AP tests last year, but still have to defend its 54.8 percent pass rate.

Some states have added a slightly better statistic -- the percentage of students in AP classes. Unfortunately, there are schools that create AP courses to impress parents but put little emphasis on the teaching and discourage the students from taking the tests. Their high percentage of AP course takers is as authentic as that Rolex you bought off a cart on F Street.

What the report cards should reveal is the percentage of students taking the AP or IB tests or the average number of tests per student. That kind of risk taking distinguishes a school. Teenagers love mountain bikes, roller coasters and scary video games. It should not be too much to ask all high school students to take at least one demanding course and test -- sell it to them as an adrenalin fix, the classroom equivalent of Tomb Raider III, something to light up any report card.

The writer covers schools for The Post's Metro section.