The -20 to 20 Student Number Lines are color coded to make it easy for students to recognize odd and even numbers. Each set of student number lines includes 30 number lines that measure 22" x 1.5" each. They also feature a write-on/wipe-away surface to make it easy for students to use over and over again. Student number lines are the perfect hands-on tool for reinforcing mathematical concepts such as counting, identifying number patterns, partitioning numbers, comparing numbers, and building number sense.