The original taxonomy of educational objectives, developed by Benjamin S. Bloom and his associates in the 1950s, was revised several decades later by a group of educationists and cognitive psychologists, who developed a revised taxonomy (RT). This article describes a Turkish study carried out among a group of pre-service teachers in order to compare the influence of the two systems on lesson planning skills. The results confirmed other studies that have indicated a number of advantages of the revised system over the earlier one.