The 24-Hour Clock

Teaching the 24-hour clock

Prerequisites: reading analogue time to five minutes and digital time, and knowing am and pm.

Suggested sequence (15–20 min)

1. Why: Show a real train timetable. “How do you know 7:00 is morning or evening?”
2. Day timeline: Walk through a day on a number line from 00 to 24, matching school times (assembly 09:00, lunch 12:15, home 15:30).
3. Rule: Introduce add/subtract 12 with the slider above, one hour at a time.
4. Practice: Use the quick quiz, then ask children to convert their own day.

Common misconceptions

• Adding 12 to morning times. Only pm hours need 12 added.
• 12:00 and 00:00. Midday is 12:00 (not 24:00); midnight starting a new day is 00:00.
• Reading 15:00 as “fifteen o’clock”. Fine as a spoken form, but link it to 3 pm.

Questions to ask

• “What time do you eat dinner? How do we write that on a 24-hour clock?”
• “How can you check your answer?” (Subtract 12 again.)

Curriculum links

UK Year 4: read, write and convert time between analogue and digital 12- and 24-hour clocks. US CCSS 3.MD.1 (telling time) and 4.MD.2 (using units of time); 24-hour time often appears in US Grade 3–5 elapsed time work.

What your child is learning

Your child is learning that the day can be counted from 00:00 to 23:59. After midday, the hours carry on from 13 to 23 instead of starting at 1 again.

Why it can feel tricky

• Children have to be sure of am and pm first.
• “Add 12” is easy, but “take away 12” needs a bit of practice.

Easy ways to help at home

• Change the clock on a phone or oven to 24-hour display for a week.
• Look at train or cinema times together: “What time is 17:45?”
• Ask your child to write their evening routine in 24-hour time.
• Keep it short and playful. 2 or 3 minutes at a time is plenty.

Try this: “Bedtime is 7:30 pm. What would the 24-hour clock say?” (19:30)