Success With Elapsed Time: Part 2

By Cassandra Hatfield, RME Assessment Coordinator

Using the number line to facilitate students understanding of elapsed time can support understanding because it is a familiar model they have used with the base 10 system. Initially, in Success with Elapsed Time: Part 1 I discussed ways to support students in thinking about elapsed time out of context and support the transition to thinking about the base 60 system of time. In this part, I will focus on three basic underlying types of contextual situations that student’s encounter with elapsed time and how to use the structure of those problems to facilitate further use of the number line.

Read through these three problems, and consider what the problems have in common and what is different about them.

1	Sam’s school starts at 7:50 am. He goes to lunch is at 12:20 pm. How much time elapses between when school starts and when he goes to lunch?
2	Jessie has soccer practice at 4:15pm. Practice lasts for 1 hour and 30 minutes. What time will practice end?
3	Michelle’s mom needs her turkey to be done for dinner at 6:30 pm. It will take the turkey 4 hours and 15 minutes to bake. What time does the need to put the turkey in the oven?

Using this model, it is clear to see that each problem has 2 of the 3 pieces of information:

Basic Structure of Elapsed Time Problems

1
2
3

In working in classrooms on this topic, I found that it was effective to give students the opportunity to brainstorm in groups and then discuss the similarities and differences between the problems as a class. The students were able to realize the structure of the problems and that one part was missing without me providing the overarching model. By giving the students the opportunity to develop the model, I became the facilitator of the learning.

As you are planning for lessons on elapsed time, plan to give students a variety of different problem types. Many traditional textbooks only offer problems with a start time and an elapsed time.

Dixon, J. (2008). Tracking time: Representing elapsed time on an open timeline. Teaching Children Mathematics, 15(1), 18-24.