Contrary to the popular song, 1, 2, 3 isn’t always as easy as A, B, C! In this course, educators dive into the nuances of how to build young learners’ number sense, problem-solving skills, and mathematical confidence through reasoning-centered instruction. Explore how counting strategies, addition and subtraction reasoning, mathematical discourse, visual models, and play-based learning support mathematical thinking in PK–2 classrooms. Throughout the course, educators will design practical lessons, instructional routines, and games that can be immediately implemented to promote meaningful engagement and deeper mathematical understanding.