Math Trailblazers is the result of decades of research and development by a team of mathematicians, scientists, education researchers, teachers, and teacher developers who are part of the Teaching Integrated Mathematics and Science (TIMS) Project at the University of Illinois at Chicago. The TIMS Project is at the forefront of current national efforts to improve the teaching and learning of mathematics and science in elementary schools. Members of the TIMS Project focus on developing tools and practices that engage learners in quantitative reasoning and modeling, especially those related to K–5 students and teachers. Project activities include teacher professional development, school outreach, curriculum development, and research into the efficacy of project programs and curricula. The program is also based on research by experts at the Learning Sciences Research Institute (LSRI) of the University of Illinois at Chicago. LSRI’s interdisciplinary researchers work to identify and solve critical learning and instructional challenges in literacy, mathematics, science, and the social sciences, and design and test innovative models, tools, and technologies to support teachers and students.