<p>Acquiring proficiency with single-case experimental designs is a critical part of behavior-analytic training. Here, I describe a simple multiple baseline-design experiment that can be conducted during a single classroom meeting using planarians as an animal model. Planarians, aquatic flatworms, are inexpensive to acquire and maintain, and they are often exempt from Institutional Animal Use and Care Committee oversight, making them ideal subjects for laboratory experimentation. The classroom demonstration takes advantage of the flatworm’s reliable movement from a lighted to a dark side of a Petri dish. This negative phototaxis results in reasonably stable baselines against which the behavioral effects of drugs may be tested. The procedures are flexible, and I describe several possible extensions for both training and research. Following the procedures described, students gain firsthand experience in experimental design, graphing, and data analysis. The activity also serves students as an empirical introduction to behavioral pharmacology.</p>