Description: One of a series of documents describing the progression of a topic across several grade levels, informed both by research on children's development and by the structure of mathematics. Measurement is the process of assigning a number to a magnitude of some attribute shared by some class of objects, such as length, relative to a unit. A combination of internalized units and measurement processes allows students to develop increasing accurate estimation competencies. Length and unit iteration are critical in understanding and using the number line in Grade 3 and beyond. Area is measured by tiling a region with a two-dimensional unit (such as a square) and parts of the unit, without gaps or overlaps.