Inquiry-based teaching helps students develop a deep, applied understanding of human–environmental connections, but most high school curricula do not use inquiry-based methods. Soil science topics, which are also generally lacking from curricula, can provide hands-on model systems for learning inquiry skills. We report on the implementation of a soil science inquiry unit for high school earth science classrooms. Teams in three classes participated in open inquiry about water runoff from, and infiltration into soils. Students learned how scientists conduct research by asking their own research questions, designing and conducting investigations, presenting findings to their peers, and peer-reviewing each other's work. Student engagement and learning were assessed through testing, final projects, a student survey, and observations of student attitudes. Pre- to post-test gains (17% average gain from 63% average pre-test score, with 71% maximum gain) showed significant student science-content-learning. Generally lower scores on final projects (61% average) than on post-tests (80% average) suggest the need for more teacher-scaffolding in complex, open-ended assignments. Students reported enjoying the unit and learning essential inquiry skills, such as experimental design, scientifically based teamwork and group-learning, and real world applicability of concepts. Observations suggest that students were motivated and substantively engaged. One-third of students reported increased excitement about science. We conclude that inquiry-based units should be more commonly used in science classrooms, to enable students to learn how to think critically, develop collaborative teamwork skills, take ownership of their learning, and be substantively engaged in authentic tasks applicable in later life.