The underwater environment presents novel challenges that can facilitate unique learning experiences for students engaged in robotics programs. Although the number of underwater educational robotics programs is small by comparison to other forms of K-12 robotics initiatives, several do exist, which have varying learning goals, implementation approaches, and tools. This chapter describes an underwater robotics program using LEGO® MINDSTORMS® components and related materials for middle and high school students. The program, known as WaterBotics™, has undergone an extensive, four-year research and development phase and curriculum redesign effort. This chapter describes the theoretical framework of the curriculum design, the components and resources available in the challenge-based curriculum, and lessons learned about teacher practices and their relationship to student learning outcomes in physical science, Information Technology skills, engineering design, and engineering career interest. “Core elements of success” of the program and curricular adaptations are described in the context of a scale-up initiative that is adapting the curriculum for use in informal education settings.