This study used data from the Third International Mathematics and Science Study (TIMSS) to determine trends in calculator use among Population 2 (13-year-olds) students in Japan, the United States, and Portugal. While relatively high levels of calculator use were observed for the U.S. and Portugal, virtually no calculator use was found in the Japanese sample. Hierarchical Linear Model analysis determined a significant negative relationship between students' frequency of calculator use and student performance in Japan. No significant relationship was detected for the U.S. and Portuguese samples. U.S. student achievement was positively associated with each of the five reported ways in which calculators are used; however, a significant negative relationship was found between student performance and Japanese students' use of calculators on tests. Plausible explanations are explored. Contains 18 references. (Author/NB)