The purpose of this study was to determine the relationship of method of presentation, grade level, sex, and achievement within grade and sex to the various bases upon which children of low socioeconomic background classify geometric concepts. Two tasks were administered to 96 subjects in the fifth, eighth, and eleventh grades--32 at each grade level. Task I was an equivalence task comprised of a sequential presentation of eight geometric concept cards. Half the subjects were given a verbal presentation while the other half were given a pictorial presentation. Subjects were asked to explain likenesses and differences between stimuli. Task II was a free sorting exercise. Subjects were presented with a 26-item picture array, asked to select from the array cards which were alike, and to explain the bases of their groupings. Task I responses were classified into Perceptible, Nominal, and Subject-Fiat categories; for Task II responses, only Perceptible, Attribute, and Nominal categories were used. This study found, contrary to expectation, that low SES children in grades 5, 8, and 11 do not vary significantly from one another in their bases of classifying geometric figures. Achievement, method of presentation, and sex were also found not to be a significant influence on bases of classification. (Author/AG)