Cal Water H2O Challenge's Classroom Challenge is a project-based, environmentally-focused competition for classrooms, grades 4-6. Designed in conjunction with NAAEE, the WestEd K-12 Alliance, and Cal Water, and aligned with the Common Core State Standards and complementary to the Next Generation Science Standards, the Classroom Challenge offers a unique opportunity for upper elementary teachers to facilitate their students’ learning of standards-based content, while developing the core understanding of environmental principles necessary to becoming science-literate citizens.