We present an alternative to the traditional classroom lecture on the topics of metabolic scaling, allometric relationships between metabolic rate (MR) and body size, and reasons for rejecting Rubner's surface "law," concepts that students have described as challenging, counterintuitive, and/or mathematical. In groups, students work with published data on MR and body size for species representing all five vertebrate groups. To support the exercise, we developed a worksheet that has students define the concept in their own words, compare different measures of MR, and evaluate plots of MR and mass-specific MR vs. body mass for both homeotherms and poikilotherms. Students also attempt to explain why selected species have exceptionally high or low MR values for their body sizes. Student feedback indicated that active learning is an effective way to learn the concepts of metabolic scaling and allometric relationships and that the opportunity to work in groups with real data stimulates interest and an appreciation for the importance of metabolic scaling to the understanding of animal physiology.