Guide · elapsed time
Elapsed Time for Kids, Made Simple
Elapsed time is how much time has passed between two times. To work it out, start at the first time and count on in jumps: whole hours first, then minutes. From 2:15 to 4:45 is two hours to 4:15, then 30 minutes to 4:45. That's 2 hours 30 minutes.
Start with what they know
Begin with one-hour jumps, which only move the short hand: an hour after 3:30 is 4:30. Then try half an hour, then quarter hours. Use real life: the film starts at 4:00 and lasts an hour and a half. When does it end? These are also the steps in our game One Hour Later.
Use a number line
A blank line works better than subtraction, because time doesn't work in tens. Write the start time at the left and the end time at the right. Make a jump to the next o'clock, then jumps of whole hours, then any minutes left. Add up the jumps. Children can see every step, and they can find their own mistakes.
The usual mistakes
Subtracting as if there were 100 minutes in an hour is the biggest one: 4:15 minus 2:45 is not 1:70. Others are counting backwards by accident, and forgetting that the hour changes when the minutes pass 60. Watching the hands sweep on a real or on-screen clock helps with all three.
How to do it with Clockwood
- Set a start time on the teaching clock and press + 1 hour or + 5 min, counting as you go.
- Print the what-time-will-it-be sheet.
- Make sure quarter past and quarter to are solid, since quarter-hour jumps depend on them.
- Ask real questions: how long until dinner?
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Questions people ask
What grade is elapsed time?
Usually third grade in the US, with simple one-hour problems earlier.
Why can't we just subtract?
An hour has 60 minutes, not 100, so normal subtraction gives strange answers across the hour. Counting on avoids that.
Coming soon to iPhone
We're building a Clockwood app with what needs a real app: every time read aloud, offline play, and a parent view of which times have stuck and which are still tricky. The full game stays free here on the web.
Coming soon on theApp Store