On a recent autumn afternoon at Harmony Leland Elementary in Mableton, Georgia, students in a fifth-grade science class investigated the essential process of classification—the act of putting things into groups according to some common characteristics or attributes. While they may have honed these skills earlier in the week by grouping their own shoes or school supplies, this class provided the unique opportunity to classify objects that are inherently fascinating to students—shark teeth fossils! This article describes how by using the teeth to estimate the length of ancient sharks, students got a classification activity they could really sink their teeth into.