Time: Clocks, am/pm and Duration
Reading the clock
Time is measured first by reading a clock. On an analogue face the short hand points to the hour and the long hand to the minutes, so a short hand just past three with the long hand at the nine reads quarter to, or 3:45. Reading a clock fluently, in hours and minutes, is the starting point for everything else about time. Year 4 reads times to the minute and writes them in the usual hour-and-minute form, the foundation for labelling them am or pm and for working out how much time passes between one reading and another.
Morning and afternoon
A day has twenty-four hours, but a clock face shows only twelve, so each time comes around twice — once in the morning and once in the afternoon or evening. The labels am and pm tell the two apart: am runs from midnight to noon, pm from noon to midnight. Seven o'clock am is breakfast time; seven o'clock pm is dinner. Without the label, 7:00 is ambiguous, which is why am and pm matter. Placing a time on the line of the whole day shows which half it belongs to and stops morning and evening being confused.
The 24-hour clock
The 24-hour clock removes the need for am and pm by numbering every hour from 00 to 23. Morning hours are the same: 9:00 am is 09:00. After noon, the hours keep counting, so 1:00 pm is 13:00, 3:00 pm is 15:00, and 9:00 pm is 21:00 — just add twelve to the afternoon and evening hours. This is the time used on timetables, computers and many clocks, because each moment of the day has one unique number. Converting between the two systems, adding or subtracting twelve, is a key Year 4 skill for reading real schedules.
How long events last
Duration is how much time passes between a start and an end, and it is found by counting on from the start time. From 9:00 to 9:45 is forty-five minutes; from 1:00 to 2:30 is one hour and thirty minutes. Counting up in convenient steps — to the next hour, then on — makes the duration easy to find without subtracting awkwardly. Duration answers practical questions: how long a lesson runs, how long until a train leaves. It is the measuring of time as an amount, rather than the reading of a single moment, and it uses hours, minutes and seconds.
The units of time
Time has its own units, and they do not go in tens. Sixty seconds make a minute, sixty minutes make an hour, and twenty-four hours make a day. These relationships are fixed and worth knowing by heart, because every duration and conversion depends on them. Two hours is a hundred and twenty minutes; half a minute is thirty seconds. Unlike length or mass, time does not use the metric tens, so the sixties and the twenty-four must simply be remembered. Knowing the units lets a child convert a duration into whatever form a problem needs.
Telling time every way
Pulling the unit together, a time can be read from a clock, labelled am or pm, written in 24-hour form, and used to work out durations. A table pairing the two systems makes the link plain: 6:00 am is 06:00, 3:00 pm is 15:00, 9:00 pm is 21:00. With clocks read to the minute, am and pm understood, 24-hour time converted, durations counted and the units of time known, a child can handle the times and schedules of everyday life — timetables, programmes and plans — which is exactly what measuring time is for.