Many upper-level undergraduate science courses are content and data laden, leaving little room for students to practice important skills such as generating hypothesis and designing experiments. This chapter introduces The Hypothesis Modification Activity—a process-based technique that employs brainstorming, synthesis, and evaluation skills. This activity provides a unique opportunity for students to propose hypotheses that address a scientific question, modify their ideas, and incorporate new information, which are critical skills for scientific thinking. For instructors, the activity is a low-burden, easy-to-implement, high-impact, active-learning technique.