Addressing the direction of high school mathematics in the 21st century, this resource builds on the ideas of NCTM's Principles and Standards for School Mathematics and focuses on how high school mathematics can better prepare students for future success. Reasoning and sense making are at the heart of the high school curriculum. Discover the components of mathematical reasoning and sense making in grades 9-12, including: reasoning habits that instruction should develop across the curriculum; key elements for reasoning in five content strands; and examples that illustrate the roles of teachers and students in the classroom specialists to reshape the conversation about high school mathematics and shift the curriculum toward an emphasis on reasoning and sense making for all students.