ACARA v9 CONTENT DESCRIPTION “recognise and use the relationship between formal units of time including days, hours, minutes and seconds to estimate and compare the duration of events”
Time is a measurement like length or mass, but its units are special: seconds, minutes, hours and days, each a fixed number of the next. Year 3 learns these formal units and the relationships between them, then uses them to estimate and compare how long events last. Unlike a ruler, where the marks are evenly spaced in tens, time mixes 60s and 24s, which is exactly what makes knowing the relationships so useful. This unit is about the units themselves and durations — how long things take and which lasts longer — rather than reading a clock face, which comes next.
The ladder of time
Time is measured in units of different sizes: second, minute, hour, day.
The smallest of these units — about one clap or heartbeat.
From seconds up to days
The four units form a ladder by size: a second is the briefest, a minute is sixty seconds, an hour is sixty minutes, and a day is twenty-four hours. Picturing them in order helps a child see that the same span of time can be named in different units — the smaller the unit, the larger the number needed. A second is about one clap or heartbeat, a minute about how long to sing a short song, an hour a television show or a lesson, and a day a full cycle of waking and sleeping. Anchoring each unit to a familiar event makes the abstract units real.
Sixty and twenty-four
Two numbers run the clock: 60 links seconds, minutes and hours; 24 links hours and days.
How many seconds make one minute?
The two numbers that matter
Two numbers run all of time-telling: sixty and twenty-four. Sixty seconds make a minute and sixty minutes make an hour, while twenty-four hours make a day. These relationships are worth knowing by heart, because every conversion and comparison depends on them. They are unusual numbers for a measuring system — length and money use tens — and that is precisely why they must be learned rather than guessed. Once a child knows sixty and twenty-four, the whole structure of time units falls into place.
Change the unit
To change a time to a smaller unit, multiply by 60 or 24.
1 hour is 1 × 60 = 60 minutes. Changing to a smaller unit means multiplying.
Changing from one unit to another
Because the units are linked by fixed numbers, a time can be rewritten in a different unit. Changing to a smaller unit means multiplying: two hours is two lots of sixty minutes, which is 120 minutes, and three minutes is 180 seconds. This converting uses the multiplication of the Number strand, applied to the special factors of time. Being able to move between units is what lets a child compare times given in different units, and it is the practical payoff of knowing the sixty and twenty-four relationships.
Which is longer?
To compare two durations, express both in the same unit, then compare.
Which lasts longer: 90 seconds or 1 minute? Put them in the same unit to be sure.
Comparing two durations
To compare how long two events last, the times must be in the same unit — just as comparing lengths needs the same unit. Is ninety seconds longer than one minute? Convert the minute to sixty seconds and the answer is clear: ninety is more. Is two hours longer than 150 minutes? Two hours is 120 minutes, which is less, so 150 minutes is longer. The method is always the same: express both durations in one unit, then compare the numbers. This is how the relationships between units let a child judge which of two events takes more time.
Estimate the duration
Estimating means choosing a sensible time and unit for how long an event lasts.
Estimate how long: clapping your hands once.
Estimating how long
Estimating a duration means choosing a sensible amount and unit for how long something takes, without timing it exactly. Clapping once is about a second; brushing teeth about two minutes; a night's sleep about nine hours; a school day about six hours. Picking the right unit is half the skill — saying a school day is six minutes or six days would be plainly wrong — and it shows a child has a feel for the size of each unit. Estimating durations, exactly as the descriptor asks, connects the formal units back to the real rhythm of a day.
Order by duration
Ordering events by how long they last is comparing their durations.
Tap the events from shortest duration to longest.
Putting events in order
Comparing more than two events means ordering them by duration, from shortest to longest: a sneeze lasts about a second, boiling an egg a few minutes, a school lesson about an hour. Ordering forces a child to judge each duration and place it against the others, using the units as a common scale. It draws together everything in the unit — knowing the units, their relationships, converting between them, and estimating — into a single judgement about time. With the units, the sixty-and-twenty-four relationships, conversion, comparison, estimation and ordering all in hand, a child can reason about how long events take, ready to read the clock that measures them in the next unit.
Quick self-check
1. How many seconds make one minute?
2. How many minutes make one hour?
3. How many minutes are in 2 hours?
4. Which lasts longer, 90 seconds or 1 minute?
5. A sensible estimate for brushing your teeth is...