(FORTUNE Magazine) – THREE-FOURTHS of all American high school seniors are qualified, at least theoretically, to go on to college. Yet a study by the National Assessment of Educational Progress found that only 51% of 17-year-olds could adequately use fractions and decimals. Not surprisingly, students in Japan, Hong Kong, Britain, and Poland outperform their U.S. counterparts on high school chemistry and physics tests. Why are American kids worldclass dunces? Perhaps because they devote too much time to watching television -- the only area in which the U.S. leads the pack. Then again, the country may not be challenging its students enough. As Chester E. Finn Jr., a professor at Vanderbilt University, says, ''At a time when European leaders are seriously considering requiring all secondary-school students to learn three languages, only 14% of our 11th-graders can write an adequate analytic piece in English.'' On the plus side, the U.S. has a wide-open educational system, allowing all students the possibility of going to college. From a young age, students in Japan and Britain, for example, are placed on either a college-preparatory track or a vocational one. Being at the top of the class requires sacrifice. In the Soviet Union, Japan, and parts of West Germany, children go to school on Saturdays and have at least a month less vacation than Americans. Full-time students in Japan and West Germany are strongly discouraged -- and sometimes even prohibited -- from taking part-time jobs. Most countries require far more homework than the U.S. does. The most rigid regimen exists in Japan, where students serve lunch to their classmates and clean bathrooms and hallways. They aren't allowed to ride motorbikes to school or to smoke cigarettes, even after school hours. The Japanese ''reward'' for survivors of grueling high school courses and university placement exams? First, a closely supervised class trip to Tokyo or Hiroshima or, for the luckier ones, South Korea, Hong Kong, or China. Then, an easier life at the university.

CHART: NOT AVAILABLE CREDIT: SOURCE: EDUCATIONAL TESTING SERVICE (ETS) CAPTION: PERCENT OF 13-YEAR-OLDS WHO SAY THEY LIKE SCHOOL

CHART: NOT AVAILABLE CREDIT: SOURCE: EDUCATIONAL TESTING SERVICE (ETS) CAPTION: PERCENT OF 13-YEAR-OLDS SPENDING TWO OR MORE HOURS A DAY ON HOMEWORK

CHART: NOT AVAILABLE CREDIT: SOURCE: EDUCATIONAL TESTING SERVICE (ETS) CAPTION: PERCENT OF 13-YEAR-OLDS WATCHING THREE OR MORE HOURS OF TV PER DAY

CHART: NOT AVAILABLE CREDIT: SOURCE: INTERNATIONAL ASSOCIATION FOR THE EVALUATION OF EDUCATIONAL ACHIEVEMENT (IEA) Source: Soviet journal, Public Education CAPTION: NUMBER OF DAYS IN THE SCHOOL YEAR

CHART: NOT AVAILABLE CREDIT: SOURCE: UNITED NATIONS EDUCATIONAL, SCIENTIFIC AND CULTURAL ORGANIZATION (UNESCO) CAPTION: SPENDING ON EDUCATION AS A PERCENT OF GNP

CHART: NOT AVAILABLE CREDIT: SOURCE: ORGANIZATION FOR ECONOMIC COOPERATION AND DEVELOPMENT (OECD) CAPTION: PERCENT OF HIGH SCHOOL SENIORS ELIGIBLE FOR UNIVERSITY

CHART: NOT AVAILABLE CREDIT: SOURCE: INTERNATIONAL ASSOCIATION FOR THE EVALUATION OF EDUCATIONAL ACHIEVEMENT (IEA) CAPTION: WHERE STUDENTS SCORE BEST ON SCIENCE TESTS