*By Cassandra Hatfield, RME Assessment Coordinator*

One of the challenges many teachers face is how to teach students to calculate elapsed time. In fact, "on the 2003 NAEP assessment, only 26 percent of fourth graders and 55 percent of eighth graders could solve a problem involving the conversion of one measure of time to another" (Blume et al., 2007).

This blog will focus on a strategy for computing the elapsed time, given a start and end time. The second blog of this series will focus on the three types of elapsed time solving story problems and how to support students in understanding the structure of those problems.

Using a procedure similar to the standard algorithm to calculate elapsed time can be challenging for students because time is in a base 60 system and depending on the times given, students have to calculate considering the change from AM and PM.

An open number line is an great tool that supports students in calculating elapsed time mentally. Before making the transition to the open number line, in a whole class setting have students count around the class by benchmarks of time and record the times on an anchor chart.

Calculating by benchmarks of time |

Calculating to benchmarks of time |

We would love to get some feedback on transitioning to a number line for calculating elapsed time. Let us know how it goes!

Blume, G., Gilindo, E., & Walcott, C. (2007). Performance in measurement and geometry from the viewpoint of Principles and Standards of School Mathematics. In P. Kloosterman & F.Lester, Jr. (Eds.), Results and interpretations of the 2003 mathematics assessment of the National Assessment of Educational Progress, 95-138. Reston, VA: NCTM.