The study was undertaken to investigate the errors made by high and low achievers in a mathematics test administered to students in their second year of high school. The focus of the study was to determine whether any common error types existed within or between the two groups or whether there were error strategies which differed between the two groups. At the same time, the results of both groups were analyzed in the light of findings which indicated that high achievers tended to make non-systematic errors while low achievers made systematic errors. The subjects were students from five secondary high schools which had been participating in the Mt. Druitt Longitudinal Study. They had participated in programs aimed at bridging the educational achievement gap between"disadvantaged" students and those who were not "disadvantaged." The intervention programs ceased in 1979 when the children had completed first grade. Since that time an aspect of the study has been the assessment of educational skills of these students as they progressed through schooling. Results suggested that a difference did exist in the error patterns of the high and low achiever groups. (PK)