Little Monkey Apps number lines.  Little Monkey Apps Number Lines, aims to teach students to visualize numbers for rote counting and ordering and to see the physical position of a number linking patterns and relationships. Unlike counters, which model counting, a number line also models measurement, which is why the number line begins with zero as you would see on a ruler. Students are also exposed to different vocabulary for addition and subtraction, such as step forward or jump back to physically suggest the movement of the frog along the number line. This free version includes ads, designed for iPad and iPhone.