Fourth graders have to know which metric unit to use in order to measure things properly. In this instructional activity on metric units, 4th graders identify when to measure in centimeters, decimeters, meters and kilometers. This instructional activity provides a quick practice of this skill. It is from the Houghton Mifflin math series and is tied to a California State Standard.   In this problem solving instructional activity, students solve 6 questions involving metric units of length with millimeters, centimeters,