Telling the Time: Why the Clock Is Hard and Time Sums Are Harder

14 September 2026 · by Larry

She reads the time off the microwave without a pause. Point her at the round clock on the wall and she goes quiet, then says "three forty-five" when it is a quarter to three.

A year or two later the clock is fine, and a different thing goes wrong. The question says the class started at 9:45 and ended at 11:20, how long was it? She writes 1 h 75 min. Or 1.75 hours. She is sure of it, because she did the subtraction carefully.

Both of these look like "not good at time". They are really two separate problems. Reading a clock face is one skill. Working out how long something took is another, and it breaks for a completely different reason. It helps to know which one you are looking at.

Part one: the clock face

A round clock asks a young child to do several unusual things at once, and none of them match how she has used numbers so far.

• Two hands, two different jobs. The short hand is the hour and the long hand is the minutes. The long hand looks more important, so children often read it first.
• The same number means two things. The 3 on the face is "3 o'clock" for the short hand and "15 minutes" for the long hand. Nothing on the clock says so.
• The minutes count in fives. Each number is five minutes further round. A child not yet steady counting in fives works each one out the slow way.
• Sixty, not a hundred. Everything else she counts goes up in tens and hundreds. The clock goes round at 60 and starts again.

The hour-hand slip

The hour hand does not jump from number to number. It creeps. At a quarter to three, it has travelled most of the way from the 2 to the 3, so it is sitting almost on the 3.

A child reads the number the short hand is closest to, sees the 3, and says three forty-five. She is an hour ahead, and she has read the hand correctly as far as she knows.

The rule that fixes it is short: the hour is the number the short hand has most recently passed, not the one it is nearest. At twenty to four, it has passed the 3 and not reached the 4, so the hour is 3 and the time is 3:40. Ask her, "Which number has it already gone past?" and let her point.

It also helps to watch it happen. Wind a real clock slowly from 2 o'clock to 3 o'clock and let her see the short hand drift across while the long hand goes all the way round. A drawing never moves, so a worksheet cannot show this.

"Past" and "to"

Children who read clocks well can still come unstuck on the words. "Quarter past four" is 4:15. "Quarter to four" is 3:45, which is not in the four o'clock hour at all. "Ten to four" is 3:50.

"To" means counting backwards from the next hour, and that runs against everything else she has been taught about reading numbers from left to right. If the words are the problem, practise just the words for a few days: say a time the long way ("twenty-five past six") and have her say it the digital way ("6:25"), then swap. Leave the clock face out until the words are steady.

Why a digital clock does not help as much as you would think

Many of the clocks a child sees at home show digits — phones, the oven, the TV box. Reading 3:45 off a screen is just reading a number aloud. It does not give her a picture of where 3:45 sits in the hour, or that it is fifteen minutes short of 4:00 — and that picture is exactly what the time sums later on need.

Part two: "how long did it take?"

This is where children who were fine with the clock start losing marks. Back to 9:45 to 11:20. The child treats the times like ordinary numbers and subtracts in columns:

11 h 20 min − 9 h 45 min. Twenty take away forty-five does not go, so borrow one from the hours and make it 120 minutes...

She has borrowed 100, not 60, because that is what borrowing has meant for years. The answer comes out as 1 h 75 min, which is not a time at all. The right answer is 1 h 35 min.

This is not carelessness. It is a correct method from the rest of maths applied to the one topic where it does not work. The same thing sits behind 1.5 hours being read as "one hour and five minutes" — the trap covered in the decimals post. Time looks like a decimal and is not one.

Count on, do not subtract

The method that almost never goes wrong is to stop subtracting and count forward from the start time in easy jumps, landing on the o'clocks:

• 9:45 to 10:00 is 15 minutes.
• 10:00 to 11:00 is 1 hour.
• 11:00 to 11:20 is 20 minutes.
• Add the pieces: 1 hour and 35 minutes.

Draw it as a line with the start time on the left, the end time on the right, and the o'clocks marked in between. Write each jump above the line. It is the same idea as a bar model: get the picture down first, then do the small, easy sums.

Counting on also handles the case that breaks subtraction completely: crossing noon. From 10:30 am to 1:15 pm, subtracting 10:30 from 1:15 makes no sense at all. Counting on is no harder than before: 30 minutes to 11:00, 2 hours to 1:00, 15 minutes more. 2 hours 45 minutes.

The other ways time sums go wrong

• Working backwards. "The show ended at 8:10 and lasted 55 minutes. When did it start?" The same number line works, jumping left instead of right: back 10 minutes to 8:00, then back the remaining 45 minutes to 7:15. Children who can only subtract in columns get stuck here fastest.
• Mixed units in the answer. The question asks for the answer in minutes and she gives 2 h 15 min. Or it asks for hours and minutes and she gives 135 min. Both are the same length of time; only one is what was asked. Circle the unit in the question before starting.
• Hours into minutes. 2 h 15 min is 2 × 60 + 15 = 135 minutes, not 215. Any time she writes a three-digit number that looks like the hours and minutes stuck together, this is what happened.

Time questions are nearly always word problems, so everything in word problems, when the sums are fine but the story is not applies here too. Most of the difficulty is deciding which times are the start and the end.

The 24-hour clock

Later in primary school, the 24-hour clock comes in; her workbook will show exactly when. The idea is small: after midday the hours keep counting instead of starting again at 1. So 13:00 is 1 pm, 18:30 is 6:30 pm, and 00:15 is a quarter past midnight.

The quick check: 12:00 is midday, so from 13:00 onwards, take 12 away to get the pm time. For durations it is actually easier, because 10:30 to 13:15 no longer has an am and a pm to juggle.

A two-minute check tonight

Three questions, in this order. Each one tells you something different.

• Set a clock to 2:50 and ask what time it shows. If she says 3:50, it is the hour hand. Go back to "which number has it passed?"
• Ask what "ten to three" means in digits. If she hesitates, it is the words, not the clock.
• Ask how long it is from 2:50 to 4:05. Do not say how. Watch what she does. If she starts subtracting columns, show her the counting-on line once, then ask a second one.

(The answers: 2:50, 2:50, and 1 hour 15 minutes.)

What actually helps at home

• Use real times, out loud. "Dinner is at 7. It is 6:40 now. How long have we got?" One question a day, at a moment that matters to her, does more than a page of drawn clocks.
• Let her own the timing of something. A TV programme, a bath, how long until the bus. "What time will it be in 25 minutes?" is a time sum she actually cares about.
• Keep a round clock where she can see it, and ask her to read it rather than your phone.
• Always count on to the next o'clock. Say it the same way every time until she says it before you do.

What does not help

• More pages of clock faces to fill in. If the hour-hand rule is not there, she is practising the slip.
• Teaching "borrow 60 instead of 100". It can work, but it asks a child to override a habit under exam pressure. Counting on avoids the habit completely.
• Racing through time questions. A timer makes a child reach for the method she knows best, which here is the one that is wrong — the same pattern described in when timing helps and when it backfires.

Where a screen fits, honestly

StudyLab's maths practice has a Primary 1 topic called Telling Time. It covers o'clock and half past only, on a drawn clock face, with the short hand drawn part of the way to the next hour mark at half past, the way a real clock shows it. The wrong choices include the hour after, so a child reading the nearest mark will pick it and find out.

Two honest limits. It does not do quarter past and quarter to, minutes in fives, durations or the 24-hour clock — for everything in part two, the number line on paper is the tool. And a drawn clock does not move; winding a real one still teaches more.

If you want to see where time sits among everything else in the early years, primary maths level by level has the short version.

The short version

• Reading a clock and working out how long something took are two different skills. Find out which one is the problem.
• The hour is the number the short hand has passed, not the one it is nearest.
• "To" counts back from the next hour: quarter to four is 3:45.
• Time sums go wrong because children borrow 100 instead of 60. That is a sensible habit in the wrong place, not carelessness.
• Count on to the next o'clock instead of subtracting. Draw it as a line.
• Circle the unit the question wants before starting.
• One real time question a day beats a page of drawn clocks.