In this activity, students quantitatively evaluate the accuracy of a classification and understand a simple difference/error matrix. Students sort birds into three possible classes based on each bird’s beak: carnivores (meat eaters), herbivores... (View More) (plant eaters), and omnivores (meat and plant eaters). Students compare their answers with a given set of validation data and generate a difference/error matrix. Students discuss how to improve their accuracy based on identifying specific mistakes they made as indicated by the difference/error matrix. The resource includes color diagrams of common birds, a data table, and four student activity sheets. The activity is part of the Land Cover/Biology chapter of the GLOBE Teacher's Guide, and is supported by Land Cover/Biology protocols. GLOBE (Global Learning and Observation to Benefit the Environment) is a worldwide, hands-on, K-12 school-based science education program. (View Less)