Math // Measurement

Comparing Time Durations

Compare durations of events and calculate the time taken by particular events or tasks

Ages
7 to 8
Type
Method
Builds on
2 topics
Leads to
1 topic
Standards
1 code

Quick check

If the learner starts cooking at 4:15 p.m. and finishes at 5:00 p.m., can they work out how long the cooking took?

Ask this to see whether the topic is secure.

Topic // Mastery

What mastery looks like

What a learner can do once this topic is secure.
  • Calculate how long an activity lasted given start and end times
  • Compare the duration of two events and identify which was longer
  • Solve a problem such as 'The lesson starts at 10:15 and ends at 11:00. How long is it?'

Topic // Map

Where this fits

What to learn first and what this topic opens up, with the reason for each link. Required links come first.
  • RequiredMust come first
  • HelpfulHelps, but not essential

Before this

2 topics

You are here

Comparing Time Durations

Ages 7 to 8 // Method

Leads to

1 topic
  • Numbers on a number lineRequired

    Measurement // Ages 8 to 9

    Prior duration comparison experience feeds into elapsed-time problem solving

Topic // Research-informed

Teaching notes

From the Marble Skill Taxonomy. These notes have not been validated in classrooms, so treat them as a starting point for your own judgement.

The approach

Children calculate how long an event lasts from its start and end times by counting ON from start to end on a number line: first bridge to the next o'clock (a number bond to 60), then add whole hours, then add the remaining minutes. Make explicit WHY column subtraction breaks when the end minutes are smaller than the start minutes, so you have to borrow across the hour (e.g. 4:10 − 2:50). Time is base-60 (60 minutes in an hour), not base-10. Comparing two durations follows from calculating each; a later end time does not by itself mean a longer duration.

Common misconceptions

  • Uses column subtraction of end minus start, which breaks across the hour boundary
  • Thinks a later end time automatically means a longer duration
  • Works in 100s not 60s (treats the minutes as base-10)
  • Counts in the wrong direction or forgets the bridging jump to the o'clock

Useful representations

  • Blank number line with jumps (to next o'clock, whole hours, remaining minutes)
  • Analogue / digital clocks showing start and end
  • Number bond to 60 for the bridging jump

Teaching practices

  • Count on from start to end via a number line: bridge to the next o'clock, add whole hours, add the remaining minutes
  • Make explicit WHY column subtraction fails when hours are crossed (60, not 100)
  • Use number bonds to 60 for the 'to the next hour' jump
  • Anchor in real start/end times (lessons, TV programmes)
  • Calculate both durations before comparing which is longer

Activities to try

  1. 1

    Build the jumps on a number line

    Why it works: Counting on from start to end — bridging the o'clock, adding whole hours, then the remaining minutes — gives the duration reliably, and column subtraction misleads across the hour unless you remember an hour holds 60 minutes, not 100.

    1. Start at the first time (e.g. 2:50) on a blank number line.
    2. Make the first jump to the next o'clock (2:50 → 3:00, a +10 jump) and say the number bond to 60 that produced it (50 + 10 = 60).
    3. Make whole-hour hops next (3:00 → 4:00, +1 hour).
    4. Add the remaining minutes (4:00 → 4:10, +10).
    5. Keep a running total of the jumps to assemble the duration (1 hour 20 minutes).
  2. 2

    Calculate then compare two durations

    Why it works: To compare durations you must calculate each one and compare the lengths; the event that ends later is not automatically the longer one.

    1. Read a problem such as 'A lesson starts at 10:15 and ends at 11:00 — how long is it?' and count on to find 45 minutes.
    2. Work a crossing-the-hour problem: 'A film starts at 2:50 and ends at 4:10 — how long is it?' bridging to 3:00, adding 1 hour, then +10 to reach 1 hour 20 minutes.
    3. Compare two events, e.g. an activity from 2:20 to 3:00 versus one from 6:15 to 6:50, by calculating each duration (40 minutes vs 35 minutes) and only then deciding which is longer.
    4. Test a tricky comparison: a 5-minute activity ending at 9:00 (so 8:55–9:00) versus one running 8:00 to 8:50 (50 minutes) — which is longer, and which ends later?

Topic // Standards

Curriculum standards

Codes for the curriculum statements this topic maps to. Each publisher owns its standard text.
The national curriculum in England: Key stages 1 and 2 framework document
Ma/KS2/Y3/M/7

Math // Measurement

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