...a public voice of mathematics education, providing vision, leadership, and professional development to support teachers in ensuring mathematics learning of the highest quality for all students. Founded in 1920, NCTM is the world's largest mathematics education organization, with nearly 100,000 members and 250 Affiliates throughout the United States and Canada.
While you're there, review the NCTM's Principles and Standards for School Mathematics:
...has four major components. First, the Principles for school mathematics reflect basic perspectives on which educators should base decisions that affect school mathematics. They then describe an ambitious and comprehensive set of goals for mathematics instruction. Finally, the document discusses the issues related to putting the Principles into action and outlines the roles played by various groups and communities in realizing the vision of Principles and Standards.