Primary 3 Maths: Perimeter and Length

Primary 3 Maths: Perimeter and Length — Tutor Lesson Plan

2026-10-27

Tutor lesson-prep guides · Primary maths

Perimeter is the walk around, not the space inside. One finger trace around a book prevents the area confusion later.

Objectives — the student can explain perimeter as the boundary length, use (l + b) × 2 and side × 4, convert between metres and centimetres, and count only the outer edges of a composite shape.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Addition	8 + 8 + 5 + 5	26
Multiplication	6 × 4	24
Units	How many centimetres in a metre?	100

02 Lesson flow (40 minutes)

Time	Stage	Tutor does	Student does
0-6 min	Walk the boundary	Trace the edge of a book with a finger	Trace and say “one lap”
6-14 min	Rectangle	(8 + 5) × 2	One alone
14-22 min	Square	6 × 4	One alone
22-32 min	Composite shapes	L-shape: outer edges only	One alone
32-37 min	Units	1 m 50 cm = 150 cm	Two alone
37-40 min	Exit check	Three questions marked at once	Finish alone

03 Teaching script (read it out)

Scene 1: Perimeter is one lap

Run a finger around the book once; the distance travelled is the perimeter.
It is not the number of squares inside, which is the area, and the unit is cm not cm².

Repeat: “perimeter walks, area fills”.

Scene 2: Rectangles and squares

8 by 5: 8 + 5 + 8 + 5 = 26, or (8 + 5) × 2.
A square has four equal sides, so side × 4.

Student does a square of side 6: 24 cm.

Scene 3: Composite shapes: outer edge only

In an L-shape, the line inside is not part of the perimeter.
Trace the outside first, then add those segments only.

Tip: colour the outer edge before adding anything.

04 Question types and worked steps

Type	Example	Steps	Answer
Rectangle	8 by 5	(8 + 5) × 2	26 cm
Square	side 6	6 × 4	24 cm
Composite	L-shape, six outer segments	Add the outer segments	26 cm
Conversion	1 m 50 cm	100 + 50	150 cm

Sanity check (teach this): For ordinary shapes the perimeter number is smaller than the area number; a perimeter of 64 with an area of 24 means the formulas were swapped.

05 Independent practice (3 questions)

Question	Answer	What to watch
9 by 4	26 cm	Using (l + b) × 2
Square of side 7	28 cm	Multiplying by 4
2 m 30 cm in cm	230 cm	Multiply by 100, then add

06 Common mistakes and what to say

Mistake	Student writes	Say this
Area answered	9 by 4 gives 36	36 is the area; the perimeter is 26 cm.
Square multiplied by 2	side 7 gives 14	A square has four sides.
Inner lines counted	adds the internal segment	Trace only the outside.
Mixed units	2 m + 30 cm written as 32 cm	Convert to one unit first.

07 Homework (paper, section and question numbers)

Primary 3 first-term paper — Section C, questions 1 to 4
Primary 3 second-term paper — Section C, questions 5 to 7

08 Exit check (last 5 minutes)

Question	Answer	Decision
9 by 4	26 cm	All right: move to area
Square of side 7	28 cm	One wrong: re-teach ×4
2 m 30 cm in cm	230 cm	Two wrong: repeat the tracing activity

09 Tutor FAQ

Formula or tracing?

Tracing first; without it the formula collides with area.

Composite shapes too hard?

Colour the outer boundary, then write each segment length; the difficulty drops sharply.

Circumference of a circle?

Not in Primary 3; that comes in Primary 6.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.