This problem-based exercise challenges students to think critically about the connection of antibiotics to cell wall structure. Without prior knowledge of antibiotics' modes of action, students are asked to deduce how the differential components of bacterial cell walls create an observed antimicrobial activity on a panel of microorganisms. Our format employs three distinct approaches to frame student understanding: first, small groups of 10 to 15 students provide a space for active discussion and peer teaching; second, students apply their knowledge to solve an activity based on an experimental scenario; finally, the process of lecture, discussion, and small groups is iterative.