The concrete, pictorial, and abstract methods of this lesson give students access to investigate, isolate, define, and use prime numbers. In this article, the authors describe an enrichment lesson that offers opportunities to investigate prime numbers in concrete, pictorial, and abstract ways. Originally introduced by Jerome Bruner in 1960, the idea that students must move through three stages (enactive, iconic, and symbolic, relabeled concrete, pictorial, and abstract) to acquire full conceptual understanding is one of the basic ideas guiding some successful mathematics curricula, including that of Singapore. This lesson centers on the elegant algorithm for efficiently isolating prime numbers from within a set of counting numbers. It presents opportunities for students to explore mathematical ideas, make and test conjectures, and engage in mathematical discussions as they become better acquainted with the concept of prime numbers. (Contains 4 figures and 2 resources.)