In 1995, the American College Testing (ACT) Program conducted a study of the effects of using a calculator in its ACT Assessment and PLAN mathematics tests taken by approximately 38,000 students. Whether there would be changes in the PLAN and ACT score scales as a result of permitting calculator use on the mathematics tests was explored with samples of 14,710 8th graders, 7,403 10th graders, 4,519 12th graders, and minority samples of 7,436 10th graders and 4,764 12th graders. Whether gender and ethnic groups would be disadvantaged by allowing calculator use was also studied. In addition, new nationally representative norms were obtained for PLAN, ACT, and the EXPLORE assessments. Results indicate that calculators may be used on the PLAN and ACT assessments without changing the meaning of the test scores. Nor was there any consistent evidence to suggest that the use of calculators disadvantages any group based on ethnicity or gender. For these reasons, the ACT has decided to allow calculator use beginning in the fall of 1996. (SLD)