Math Background

Lesson: Figuring Elapsed Time
Introducing the Concept

In this lesson, students explore elapsed time in hour intervals.

Materials: large clock with moveable hands for class display

Preparation: If a commercial educational clock face 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 five minutes.

  • Show 4:00 on the clock.
  • Ask: What time does the clock show? (4:00)
  • Move the minute hand around the clock one time and move the hour hand to show 5:00.
  • Ask: Now what time does the clock show? (5:00) How many times did I move the minute hand around the clock? (one time) How much time passed from 4:00 to 5:00?
    Some students may say 60 minutes. Reinforce that 60 minutes equals 1 hour.
  • Ask: How did I move the hour hand to show that 1 hour passed?
    Students should have observed that you moved the hour hand from 4 to 5.
  • Ask: How many times should I move the minute hand around the clock to show the time after 3 hours have passed? (three times)
    Have the class count hours as you move the minute hand around the clock three times.
  • Ask: How should I move the hour hand to show the time in 3 hours?
    Have the class count hours as you move the hour hand from 5 to 8.
  • Ask: What is the time? (8:00)
  • Repeat the steps above for 1:00 to 3:00 to 4:00, and for 7:00 to 11:00 to 2:00. Then show 2:30 on the clock. (Make sure the hour hand is halfway between the 2 and the 3.)
  • Ask: What time does the clock show? (2:30) Why is the hour hand halfway between 2 and 3?
    You may need to remind students that when the time is half past the hour, the hour hand is halfway between two numbers.
  • Move the minute hand around the clock one time and move the hour hand so it is halfway between 3 and 4.
  • Ask: Now what time does the clock show? (3:30) How many times did I move the minute hand around the clock? (one time) How much time passed from 2:30 to 3:30? (1 hour)
    Explain to students that one rotation of the minute hand around the clock is equal to 1 hour, no matter where the rotation begins.
  • Ask: How did I move the hour hand to show that 1 hour passed? (from halfway between 2 and 3 to halfway between 3 and 4)
  • Ask: What time will it be in 4 hours? (7:30)
    Have the class count hours as you move the minute hand around the clock four times and move the hour hand to halfway between 7 and 8.
  • Repeat these steps for 6:15 to 9:15 to 11:15, and for 5:50 to 7:50 to 12:50. Encourage students to watch the movement of both the minute hand and the hour hand as they read the times on the clock.
Houghton Mifflin Math Grade 3