Grade 4: Elapsed Time

Warm up with a quick recall on the board. Count on from the start time to the next hour, then add the remaining minutes, using a number line of times. Bridge over the hour carefully.

Elapsed time is how long something lasts: the gap between a start time and an end time. It is harder than reading a clock because time is not base ten, there are 60 minutes in an hour, so students cannot just subtract the numbers. Counting on in friendly jumps is the reliable method. Model the method clearly, thinking aloud:

• Make sure telling time is secure first, since elapsed time depends on reading both the start and the end.
• Count on rather than subtract. From 2:15 to 3:45, jump 45 minutes to 3:00, then 45 minutes to 3:45, giving 1 hour 30 minutes.
• Use a number line marked with times, so each jump to the next whole hour is visible.
• Teach the hour boundary carefully: you cannot borrow ten, an hour is 60 minutes.
• Progress to problems that cross the hour, then across midday and midnight.

Work this through step by step on the board, then have the class talk you through a second one.

• How long from 2:15 to 3:45?
• 2:15 --> 3:00 is 45 min
• 3:00 --> 3:45 is 45 min
• total: 45 + 45 = 90 min = 1 h 30 min

Do the first few questions of the practice worksheet together, one child explaining each step. Check for understanding before releasing the class to work alone.

Students complete the worksheet independently. Hand out the three difficulty levels below so every child works at the right stretch.

Circulate and look for these, they are the usual sticking points:

• Subtracting the times like base-ten numbers (3:45 - 2:15 done as 145 minus 215).
• Forgetting there are 60 minutes in an hour, not 100.
• Losing an hour when the times cross midday or midnight.
• Mixing up the start and end times.
• Subtracting times like plain numbers (treating 60 minutes as 100) and losing track when crossing the hour.

Pull the class back together. Ask one child to explain elapsed time in their own words, pose a single check question everyone answers on a mini whiteboard, and name what you will build on next lesson.

Use the independent worksheet as the evidence. A child who can complete it accurately and explain one answer has met the objective; anyone who cannot needs the easier level and a short reteach next session.