The similarity between two scales for assessing socioeconomic status was examined from longitudinal data on the achievement of Canadian students. Toronto's Longitudinal Study of Achievement sampled the complete senior kindergarten population (8,679 5-year-olds) in 1961-62, classifying father's occupations according to Hollingshead and Redlich's scheme. A 1970 followup asked 3,607 students to name their father's and mother's current jobs, and classified them according to Blishen's scale, a Canadian scale that is based upon weighted average of mean income and mean education for every occupational category in the census. When the same information was requested in 1975, several problems arose: different persons represented the head of household; there was no code available for certain occupations; and special categories had to be created. A number of changes were noted, over the years; occupational stability was more frequent in certain occupational categories. It was tentatively concluded that it does not make a great deal of difference which socioeconomic scale is used in achievement studies. Since one cannot assume status directly from occupation, it is not a relevant predictor of achievement. Place of residence, immigration status, and language may be more productive environmental variables to study. (GDC)