A strong foundation in early number concepts is critical for students' future success in mathematics. Research suggests that visual representations, like a number line, support students' development of number sense by helping them create a mental representation of the order and magnitude of numbers. In addition, explicitly sequencing instruction to transition from concrete to visual to abstract representations of mathematics concepts supports students' conceptual understanding. This column describes and illustrates how teachers can use number lines and features of explicit and systematic instruction to support students' early development of number sense.