Marine litter is a global environmental problem, and working with educators and school students has much potential to facilitate greater public understanding of the solutions and to enable action. This research examined two new educational activities designed to empower European educators and school students to engage with the topic of marine litter, particularly focusing on behavior and on known determinants of behavior rather than knowledge alone. In Study 1, 120 educators participated in an online training course on marine litter, and completed a pre- and post-course questionnaire to assess change. After participating in the course, educators felt significantly more skillful and confident to incorporate marine litter education into their future teaching. In Study 2, 341 school students (7–18 years old) participated in an educational video competition on marine litter, and completed a pre-post questionnaire to assess change. Following the educational activity, students were more concerned about marine litter, had a better understanding of the issue, causes and impacts, and reported performing more waste-reduction behaviors. This research brings together educational and behavioral literatures and demonstrates how educational activities can be documented and evaluated systematically in the quest of tackling marine litter.