This investigation of the possible effects of using calculators in mathematics teaching was based on an analysis of the cognitive and affective aims of mathematics education in the nine-year comprehensive school in Finland attended by all children aged seven through fifteen. The experiment consisted of a comparison of two fourth-grade classes using calculators with three control classes. Calculators were used in about 25 percent of the mathematics lessons of the experimental group during the study period. Results indicated posttest differences favoring the experimental treatment significant at the p < .05 level on understanding, application, and attitude tests. In addition, it was apparent that the lowest ability group seemed to profit considerably more than the others from the use of the calculator. (MP)