A variety of explanations for the decline of Scholastic Aptitude Test (SAT) scores over the past several years are examined. Studies undertaken by the College Board indicate that the SAT score decline has not eroded the test's validity, that the decline is not an artificial by-product of score-equating techniques, and that it is not to any appreciable extent an artificial by-product of changing test-taking patterns. Further investigation has shown that even the first decline of SAT score averages can not be explained by either an expansion in the population of immediate college entrants or an expansion in the population of SAT-takers. In fact, the increased overall population does not seem to have become less able, and the expansion in the smaller SAT-taking population seems to have paralleled expansion in the population of immediate college entrants since 1964. The data are insufficient to either confirm or deny that a change in the socioeconomic balance of the test takers is a possible cause. The evidence does not indicate that there has been a general decline in reasoning ability among the student population. Tables present score data for the high school classes of 1956 through 1974, and the implications for college administrative planning are briefly discussed. (Author/MV)