Not all educators agree that the best ways to teach mathematics include giving students electronic calculators. But many do, and their view is reflected in the policies and practices of school districts, textbook publishers, testing companies, and state education agencies. That adds up to profits for Texas Instruments Inc., the Dallas-based semiconductor manufacturer that invented the hand-held calculator 40 years ago and dominates the school market for the devices today. This article examines the factors that still make Texas Instruments the leader in school calculator market after four decades of operations.