Time: 12-Hour and 24-Hour Clocks

Lesson 1 of 2

In this lesson:

• Read and tell time on both 12-hour and 24-hour clocks
• Convert times between the two systems
• Find duration using the count-up method

Four Learning Outcomes for Today

By the end, you can:

1. Read and tell time on 12-hour and 24-hour clocks
2. Convert any time between the two systems
3. Identify midday and midnight correctly
4. Find duration using the count-up method

Prerequisite: read a clock face; know 60 min = 1 hr.

Clock Reads 3:00 — Morning or Afternoon?

A clock face shows 3:00.

• Hour hand points at 3
• Minute hand points at 12
• Morning or afternoon? Can you tell from the clock?

The hands look exactly the same at 3 a.m. and 3 p.m.

Two Facts That Power This Lesson

Two things you already know:

• 60 min = 1 hr — powers every conversion and duration here
• 24 hrs = 1 day — the 24-hour clock counts every one

Hold this: school starts 8 a.m., ends 3 p.m. — how many hours? We'll answer it by the end.

Which Half of the Day? Sort These Events

You reached for a.m./p.m. to sort them. The 24-hour clock removes that need.

The 24-Hour Clock: Counting Straight Through

Counts from 00 to 23 — no repeat, no a.m./p.m. needed.

• Written as four digits: two for hours, two for minutes
• Hours always two digits: 7 a.m. → 07, not 7
• Examples: 0830, 1405, 2315

0000–1159 = morning; 1200–2359 = afternoon or evening.

The Full Day in One Picture

The left half (teal) is a.m. — midnight to midday. The right half (yellow) is p.m. — midday back to midnight.

Five Landmark Times Worth Memorising

p.m. times always above 1200. a.m. times keep the same hour digits.

Check-In: Write These in 24-Hour Form

Write each time in 24-hour notation:

1. 9:00 a.m.
2. 3:00 p.m.
3. 12:00 midnight (tricky — attempt it, we'll confirm soon)

Pause and write your answers before the next slide.

You Know Both Systems — Now Convert

You can read times in both 12-hour and 24-hour form.

The next question is practical: a timetable shows 1430 — what's that in 12-hour? A friend says "meet me at 2:30 p.m." — what's that in 24-hour?

This chunk builds the conversion skill.

Two-Case Conversion: 12-Hour to 24-Hour

Step 1: Sort — before noon or after?

Before noon (a.m.): keep the hour, two digits

• 7:15 a.m. → 0715; 9:05 a.m. → 0905

After noon (p.m.): add 12

• 2:30 p.m. → 1430; 11:20 p.m. → 2320

Day-Strip: Midnight and Midday Anchors

Midnight sits at the left edge (0000). Midday sits exactly at the centre (1200). Both resist the "add 12" habit — learn them as fixed anchors.

Tricky Points: Midnight and Midday Fixed Anchors

Midnight = 0000. Midday = 1200. Learn both as facts.

Worked: Conversion in Both Directions

12-hour → 24-hour:

• 7:15 a.m. → 0715 (keep hour)
• 2:30 p.m. → 1430 (add 12)

24-hour → 12-hour:

• Hour 13–23: subtract 12 + p.m. → 1745 = 5:45 p.m.
• Hour 00–11: a.m. as written → 0920 = 9:20 a.m.

Predict First — True or False?

A learner writes: 7:00 a.m. = 1900.

• Is this correct or incorrect?
• If incorrect, what error did they make?
• What is the correct 24-hour form of 7:00 a.m.?

Write your answer and explanation before advancing.

Resolving the Add-12 Error on 7 a.m.

7:00 a.m. = 1900 is INCORRECT.

The learner added 12 to a morning time.

• 7:00 a.m. is before noon → keep the hour → 0700
• 1900 is evening; 7 a.m. cannot be there

Only p.m. gets +12. Morning hours stay unchanged.

Guided Practice: Two Tricky Conversions

Try both — one rule, one fixed anchor:

1. Convert 6:45 p.m. to 24-hour form.
2. Convert 12:00 midnight to 24-hour form.

Write your working for each. Midnight does not use the rule.

Duration: Count Up, Not Subtract

Duration = the gap between a start and an end time.

Clock minutes borrow 60, not 100 — subtraction gives wrong answers.

Three hops instead:

1. Start → next whole hour
2. Count whole hours across
3. Add leftover minutes

Worked: Bus Journey 0830 to 1115

Prepare: Write Each Hop First

Lessons end at 1300 and after-school club starts at 1415.

Before solving the full problem, write down each hop:

• Hop 1: 1300 → ____ = ____ min
• Hop 2: ____ → 1415 = ____ min

Write individual hop values before combining. This makes errors visible.

Your Turn: Film Duration (No Scaffolding)

A film starts at 7:45 p.m. and ends at 9:20 p.m.

1. Convert both times to 24-hour form first.
2. Then count up from start to end.
3. Write the total duration in hours and minutes.

No hints this time — work all steps independently.

Key Facts and Misconception Warnings

✓ 24-hour: 00–23, four digits always

✓ a.m. → keep the hour; p.m. → add 12

✓ Midnight = 0000; Midday = 1200 (fixed facts)

✓ Duration: count up in hops — never subtract

Only p.m. gets +12 — never morning times

Midnight is 0000, not 1200

Coming Up: Timetables and Overnight Durations

In the next lesson:

• Read travel and school timetables in 24-hour format
• Find durations that cross midnight — one extra step in the count-up
• Apply today's skills to multi-stop journeys

The four-digit form and count-up method from today are the foundation.