This document discusses measuring the impact of informal science learning. It notes that informal science programs aim to achieve goals like inspiration, engagement, encouraging students to study science, and developing a world-leading scientific workforce, but that the effect varies for each person. It also discusses the challenges in measuring impact given that different programs have slightly different aims. Examples are provided of potential impacts, like increasing students' interest in and confidence with science. The importance of informal science in developing skills, confidence, and passion for learning science is discussed.