To investigate how the number of years students spend studying academic subjects affects their achievement, this study compiled data from a nationwide longitudinal study of 58,000 high school students begun in 1980, and from 1982 College Board testing files. Years of instruction in seven subject areas were related, using statewide averages, to verbal and mathematics achievement test scores. Populations compared were students in academic, general, and vocational tracks, in New York, Pennsylvania, Ohio, Illinois, California, and Washington, and those taking and not taking college admission tests. It was found that (1) New York and Pennsylvania students received more academic instruction than those in the other states; (2) the pattern of test scores related inconsistently to that of course taking; (3) among SAT takers that completed any of three achievement tests, New York students registered both the most courses and the highest aptitude and achievement scores; (4) verbal and math aptitude scores and course taking all related similarly to achievement scores in New York and California; and (5) course offerings and requirements and tracking policies strongly affect students' exposure to course content. (MCG)