Elapsed Time - What Time Will I Get Home?

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SWBAT use number lines to calculate elapsed time.

Big Idea

Applying the measurement of elapsed time to a person's daily schedule helps students understand the reason for understanding time.

Warm Up

5 minutes

During the warm up, I review elapsed time as well as a the number line.  I explain one of the reasons we need to understand elapsed time is for our own daily schedule.  Each person has different responsibilities and activities to do each day. 

I describe my daily schedule, showing students how I have it typed out.  I tell students what time I wake up and walk the dog, which is 5:30.  I map out the day, sharing everything I do including getting ready, driving my son to school, driving to my school, and the time we spend in each subject area at school, after school classes, and meeting with teachers. I explain that my family needs to know what time I will be home at the end of the day. 

The students are going to try and figure out what time I will be home today, using a number line to calculate elapsed time. 

Partner Work

30 minutes

Working in partners, the students find their "spots" throughout the room, and begin discussing and calculating how to determine the elapsed time. They do this by adding to reach benchmark numbers of five and ten minute increments, and then adding on any remaining minutes. 

In the video below, the students explain how to the hour changes once they reach 60 minutes. Having students explain this concept demonstrates their understanding of elapsed time.  Later in the video these two students discuss how to add a minute at 6:39 to reach the benchmark of 6:40 to continue adding the remaining minutes.  


The students are using place value by decomposing numbers in order to create "friendly numbers" to add. The students draw their own open number lines. Some students start a new line for each step, and some continue until they fill up the space on a number line before beginning a new number line.  

I demonstrate for the students the importance of writing the activity name under the time to help them keep track of their progress, because their papers will be filling up with different times.  

They continue with the process until they find the time that I will be home, which in this scenario is 6:14 p.m.

Wrap Up

10 minutes

Based on my observations while the students are working with their partners, I noticed some errors in calculating the time.  Even though the students add very accurately, the application to adding time is more difficult because of their lack of experience with using clocks.  

To clarify the times of the activity and the ending time, I decided to use individual analog clocks with the class to find the elapsed time of activity.  The student clocks have the minutes marked clearly which provide the students to opportunity to use the skill of moving to a benchmark counting number and breaking apart a number with place value.  This also allows them to experience how time changes as it passes the hour marks. which was a concept that confused them when they only used addition.