Mastering 24-Hour Time

Overview

Age group: Year 4 (8-9 years)
Duration: 30 minutes
Class size: 30 pupils
National Curriculum link:

• Mathematics Program of Study, Year 4
• Measure – Time: Pupils should be able to “read, write and convert time between analogue and digital 12- and 24-hour clocks.”

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Learning Objectives

By the end of the lesson, pupils will:

• Understand the concept of the 24-hour clock as an extension of the 12-hour clock.
• Convert times from the 12-hour (am/pm) format to 24-hour format and vice versa.
• Explain and justify their reasoning when converting between these time formats.

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Success Criteria

Pupils will be able to:

• Identify whether a 24-hour clock time is before or after midday.
• Correctly convert times from 12-hour to 24-hour clock and back.
• Use key vocabulary such as “midday,” “midnight,” “am,” “pm,” “hours,” and “minutes.”
• Explain the reasoning behind their conversions using sentence stems like:
  • "I know the time is ___ because..."
  • "I convert ___ to 24-hour time by..."
  • "This time is different from ___ because..."

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Resources

• Whiteboard and markers
• Pre-prepared time cards (showing both 12-hour and 24-hour times)
• Individual mini whiteboards and pens for pupils
• Digital timer (e.g., phone timer)
• Worksheets with graduated difficulty tasks

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Lesson Structure

1. Engaging Introduction (5 minutes)

• Contextual Hook:
  Start by showing a video clip or image of an airport departure board displaying times in 24-hour format. Ask:
  • “Has anyone seen times like this before? What do you notice that’s different from a wall clock?”
• Initial questioning:
  • “How do you think the 24-hour clock might help us when travelling?”
  • “What might be tricky about understanding or using this clock?”

Build curiosity around why 24-hour time is important in real life (trains, planes, hospitals).

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2. Teaching & Modelling (12 minutes)

Step 1: Explain 24-hour time

• Model using the White Rose Maths approach:
  • Write times in 12-hour format: 3:00 pm
  • Ask pupils to identify if it is morning or afternoon.
  • Show the corresponding 24-hour time: 15:00.
• Explain:
  • For any time after midday (12pm), you add 12 to the hour.
  • For times between midnight and midday, the 24-hour clock is the same apart from midnight which is 00:00.

Targeted Whole-Class Questions (Bloom’s Taxonomy - Apply, Analyse, Evaluate):

• “Why do we add 12 for times after midday?”
• “Can you explain, in your own words, how you would convert 7pm to 24-hour time?”
• “If the time is 00:30, what does this tell us about the time of day? How do you know?”

AfL 1: Mini Whiteboard Check
Use a quick ‘show me’ activity with mini whiteboards:

• Pose a time in 12-hour format (e.g., 8pm) and ask pupils to write the 24-hour equivalent.
• Collect and scan for misconceptions. Use this to gauge whole-class understanding quickly.

Step 2: “Prove it” Reasoning Modelling

• Pose a challenge: “Is 12:00 midnight written as 12:00 or 00:00 on the 24-hour clock? Explain your thinking.”
• Model with sentence stems, e.g.,
  • “I think it is ___ because _____.”
• Set a 1-minute timer for pupils to discuss reasoning with a partner, then share with class.

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3. Guided Practice and Gradual Complexity (8 minutes)

Layered tasks on worksheet:

1. Convert simple times (e.g., 1pm, 6am) to and from 24-hour format.
2. Convert mixed times including midday (12pm) and midnight (00:00 / 12am).
3. Compare two times - "Which is earlier, 16:30 or 4:45pm? How do you know?"
4. Problem-solving: “A train leaves at 14:15 and arrives at 17:45. How long is the journey? Explain using 24-hour times.”

Active Reasoning Questions during task:

• “Can you explain how you worked out if a time is morning or afternoon?”
• “Why do you think the 24-hour clock might be easier for timetables?”
• “What mistakes might someone make converting 12pm and 12am? How do you avoid them?”

AfL 2: Peer Marking and Reasoning Feedback

• Pupils swap answers and use sentence stems to justify if their partner is correct or not:
  • “I think you are (right/wrong) because...”
• Teacher circulates to listen and prompt deeper explanations.

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4. Plenary (5 minutes)

• Use a quick round of “Explain your thinking” using a couple of time challenges on the board:
  • Example: “Convert 11:00 pm to 24-hour time.”
• Random pupils explain out loud using the sentence stems. Timer used to keep explanations concise.
• Address common misconceptions:
  • 12pm vs 12am confusion
  • Forgetting to add 12 after midday
• Finish with the question:
  • “Why do you think learning 24-hour time is important for life outside school?”

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Common Misconceptions & Difficulties

• Confusing 12:00 noon (12pm) and midnight (12am) when converting.
• Forgetting to add 12 to the hour after midday.
• Thinking 00:00 is 12am but writing 24:00 instead (which is not valid).
• Difficulty understanding why times after noon continue past 12 on a clock rather than restarting at 1.
• Mixing up which times belong to am and pm in the 12-hour system making conversion errors.

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Links to White Rose Maths Scheme

• This lesson aligns with the White Rose Year 4 Autumn Block 2: Measure: Time.
• The lesson’s focus on conversion between 12-hour and 24-hour clocks directly supports the scheme’s emphasis on telling and writing time from analogue clocks and converting between different time representations.

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By scaffolding the lesson with engaging real-world context, targeted questioning for reasoning, active peer discussion, and carefully designed tasks that increase in complexity, this lesson ensures pupils not only know how to convert times but can confidently explain their understanding and uncover common pitfalls.