The University of Chicago’s Center for Elementary Mathematics and Science Education and the University of Illinois at Urbana-Champaign’s College of Education propose a two-year STEM+C Track 1 Exploratory Integration project, "EI: Learning Trajectories for Integrating K-5 Computer Science and Mathematics," which will create prototype learning trajectories for computer science at Grades K-5. Each trajectory will span multiple grades and will include a target goal, intermediate objectives, performance expectations, sample tasks and assessments, and hypothetical learning paths. The prototype learning trajectories, including the sample tasks and assessments, will be designed to fit with Everyday Mathematics 4 (EM4), the elementary curriculum from the University of Chicago School Mathematics Project. Since EM4 is newly revised to closely align with the Common Core State Standards for Mathematics (CCSS-M), the tasks and assessments will also be usable with other instructional materials aligned with CCSS-M. The learning trajectories (LTs) will be developed and tested in collaboration with 18 teachers and 4 teacher-leaders in public schools in Champaign, Illinois.