The focus of this unit is the extension of linear measurement to the measurement of time. To compare durations, standard units are needed like hours, minutes, and seconds and these can be decomposed, added, seen as fractional pieces of a larger unit (for example, half an hour), or exchanged—for example, 30 minutes can be exchanged for half an hour. The teaching of time has often been misconstrued as the “telling of time.” Being able to read and recite time from the face of the clock does not mean that children understand time, the passing of it, or the mathematics involved in the measuring of it. This unit is crafted and sequenced carefully to foster those understandings.