Cognitively Guided Instruction (CGI) is a professional development program based on an integrated program of research focused on (a) the development of students’ mathematical thinking; (b) instruction that influences that development; (c) teachers’ knowledge and beliefs that influence their instructional practices; and (d) the way that teachers’ knowledge, beliefs, and practices are influenced by their understanding of students’ mathematical thinking. Using CGI strategies is an effective way of implementing the Iowa Core Curriculum for Mathematics at the elementary level.