Constructivism is currently a hotly debated topic, with proponents and opponents equally adamant and emotional with respect to their viewpoints. Many misconceptions exist on both sides of the debate, and misuses of terminology and attribution are rampant. Constructivism is a theory of learning, not a particular approach to instruction and not a curriculum. Proponents, the majority of whom are involved in K-12 education, argue that reaching more students with a deeper understanding of mathematics requires an appreciation of how knowledge is constructed and an instructional approach that more fully acknowledges the students' roles as active participants in the classroom instruction, rather than the lecture method which has worked well for some but poorly for others. The opponents, many of whom are mathematicians, tend to equate constructivism with "discovery" learning and deem it as inefficient at best, and tolerating inaccurate mathematics at worst. However, many mathematicians, including those who criticize constructivism, revere R. L. Moore as an outstanding teacher of mathematics. The Moore Method and the Modified Moore Method are frequently cited as exemplary in the literature on teaching undergraduate- and graduate-level mathematics. An analysis of his method of teaching, however, indicates adherence to a theory of learning which he did not necessarily articulate, and might even have disputed. The goal of this article is to show that Moore's method aligned with a constructivist approach.