Pattern recognition is a critical component of success in mathematics. Students at all levels should be provided with opportunities to investigate and uncover patterns throughout their mathematical careers. Further, they should be allowed to explore situations in which pattern recognition plays a vital role in the construction of important mathematical knowledge. This article will discuss a lesson that introduces arithmetic sequences through a simple, yet rich exploration of a pattern. This lesson has been taught in a methods course for secondary mathematics teachers to provide them with a model of a constructivist lesson that they will be able to implement in their own classrooms when they begin teaching. It is, also, beneficial to this group as it affords them an opportunity to participate in a cooperative learning activity that lends itself to a wide variety of solution methods. (Contains 4 figures.)