Today's lesson is the second part of "How Time Flies". As the students just learned to use the number line (MP4, MP5) to calculate elapsed time, I decide to have one more day of purposeful practice. If your students, like mine, have been using open number lines efficiently to add and subtract then a second practice day may be all that's needed. If telling elapsed time is the first opportunity your students have had to use number lines, I strongly recommend that you practice adding and subtracting on number lines first, and then transfer that developing understanding to using an open number line for adding and subtracting, before attempting to use it to calculate elapsed time.
This video of students describing elapsed time on a number line may be helpful.
I warm the students up by asking them to share some of their family's schedules the night before. We work as a class to figure out the elapsed time for these situations using number line skips on the board (MP7, MP8).
I then present the attached page of word problems to the children and discussed the directions.
As the students work, I confer with individuals, or small groups. I am listening for precise language when the students are explaining their work to me, as well as watching for efficient use of the number line tool (MP3, MP6).
This student was able to compute the elapsed time but had his clock set wrong (MP1, MP2). All he needed was a few prompts to help him stay organized.
As this student worked, I notice she wasn't using a number line. However, I thought her strategy was an intelligent one, as she communicated strong number sense in her explanation.
This problem was a bit tricky for many students, as it requires them to subtract time. This student uses a combination of strategies.
In order to close this task, I remind students that we will need to use elapsed time during our bat house project. I alert the children to the idea of making a schedule for our building day and for that, calculating elapsed time will be essential.
I have also created a practice page for home, which includes them writing their own word problem for others to solve the next day.