The document discusses teaching mathematics concepts through big ideas and problem solving. It describes big ideas as large networks of interrelated concepts that students understand as whole chunks. Teachers should explicitly model big ideas and have students actively discuss and reflect on them. Examples of big ideas in geometry include properties of shapes and geometric relationships. The document provides strategies for structuring the classroom and lessons to encourage problem solving, communication, and assessing student understanding of big ideas through observation, interviews, student work and self-assessment.