Between 1959 and 1960 the mean scores obtained by all candidates on the Advanced Placement Examinations in Literature and English Composition, American History, Chemistry, and Mathematics declined from .2 to .6 points on a five-point trading scale. The primary purpose of the study was to determine if the observed decrease in mean scores was due simply to an influx of candidates from schools new to the program or if the decrease was also characteristic of the level of performance of candidates from schools which have been in the program for some time. The basic data consist of the scores obtained on the 1959 and 1960 examinations by samples of candidates drawn from schools which have been in the program for varying lengths of time. Three groups of schools are considered, (1) those which have been in the program since 1956, (2) those which entered the program in 1957 or 1958, and (3) those which supplied candidates for the first time in 1960. Separate analyses are made for schools in New York State and for schools in all states other than New York. The data indicate that (1) candidates from the new schools did less well on the average on the 1960 examinations than did candidates from the older schools, (2) candidates from the older schools did less well on the 1960 than on the 1959 examinations. In an effort to account for the decline in the mean performance of candidates from the older schools between 1959 and 1960, the SAT scores of spaced samples of students from these schools were obtained for the years in question. The observed declines in scores cannot be accounted for in terms of changes in the scholastic aptitude of candidates.