Two groups of 32 educable mentally retarded children (ages 7 to 14 years) were compared as to their arithmetic and classification performances attributable to the presence or absence of a 4 1/2 week exposure to classification tasks. The randomized block pretest-posttest design was used. The experimental group and the control group were matched on their arithmetic skills prior to the experiment. It was found that arithmetic post-test scores covaried significantly with arithmetic pre-test scores and classification pre-test scores and that classification post-test scores covaried significantly with age and classification pre-test scores. The experimental group showed significantly higher post-test performances on arithmetic and classification over the control group, indicating that the classification exposure treatment facilitated the acquisition of arithmetic as well as classification skills. (Author)