Math Background

Lesson: Figuring Elapsed Time
Developing the Concept

In the previous lesson, students learned to find elapsed time in hour intervals. Now they will explore elapsed time in five-minute intervals.

Materials: large clock with moveable hands for class display

Preparation: If a commercial educational clock is not available, make your own, or use Learning Tool 21 in the Learning Tools Folder.

Prerequisite Skills and Background: Students should know how to tell time to the hour and to five minutes.

  • Show 2:15 on the clock.
  • Ask: What time does the clock show? (2:15)
  • Move the minute hand forward and adjust the hour hand to show 2:35.
  • Ask: Now what time does the clock show? (2:35) How long does it take the minute hand to move from one number to the next? (5 minutes) How much time passed from 2:15 to 2:35? (20 minutes)
    Point to 2:20, 2:25, 2:30, and 2:35 on the clock as you count aloud with the class, “5, 10, 15, 20.”
  • Ask: Did I move the hour hand very far?
    Students should notice that you didn't move the hour hand very far because only 20 minutes passed.
  • Ask: What will the time be in 15 minutes? (2:50)
    Have the class count by fives to 15 as you move the minute hand from 2:35 to 2:40 to 2:45 to 2:50.
  • Ask: How far should I move the hour hand?
    Elicit from students that you should move the hour hand only slightly because only 15 minutes passed.
  • Repeat the steps above for 6:10 to 6:20 to 6:50, and for 9:05 to 9:50 to 9:55. Then show 12:00 on the clock.
  • Ask: What time does the clock show? (12:00)
  • Show 1:00 on the clock.
  • Ask: Now what time does the clock show? (1:00) How much time passed from 12:00 to 1:00?
    Students should easily recognize that 1 hour passed.
  • Show 1:30 on the clock.
  • Ask: What time does the clock show now? (1:30) How much time passed from 1:00 to 1:30?
    Students should realize that 30 minutes passed. If not, have them count by fives from 1:00 to 1:30.
  • Ask: How much time passed from 12:00 to 1:30?
    Lead students to discover that from 12:00 to 1:00, 1 hour passed, and from 1:00 to 1:30, 30 minutes passed, so from 12:00 to 1:30, 1 hour and 30 minutes passed.
  • Repeat these steps for 3:00 to 6:30.

Wrap-Up and Assessment Hints
Give students many opportunities to practice finding elapsed time on their own clocks. If commercial educational clocks for individual students are not available, give them copies of Learning Tool 21 from the Learning Tools Folder so they can make their own clocks. Encourage students to focus on the positions of both the minute hand and the hour hand when they find elapsed time. While this may be challenging for them at first, they will soon see the relationship between the movement of the two hands. When you assess students, have them count aloud as they find elapsed time in hours and five-minute intervals. This will help you better evaluate their understanding of the concept.

Houghton Mifflin Math Grade 3