Primary 1 Maths | Direct Length Comparison Guide | Align One End, Three Wordings, One Unit

2026-11-09

Tutor lesson-prep guides · Primary Maths

A child holds one pencil in each hand and says the blue one is longer. Eyesight is fine; the starting points are not. Until both objects share one end, the comparison does not count.

Objectives — Students can: (1) place one end of both objects against the same line or table edge; (2) state the result as longer than, shorter than, or the same length; (3) measure two objects with the same non-standard unit, such as paper clips or squares, and compare using the counts.

01 Prerequisites (3-minute check)

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

Skill	Quick check	Pass mark
Numbers to 20	Count from 1 to 20	Counts and writes the numerals
Comparing amounts	Which is more, 5 sweets or 7 sweets	7
Straight lines	Trace a straight line along the table edge	Can draw a straight line

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-6 min	Wrong demo	Deliberately offset two pencils and ask which is longer	Say what is wrong
6-16 min	Align one end	Press both left ends to one line, then look at the right ends	Align three times
16-28 min	Three wordings	Longer than, shorter than, the same length	Say each one
28-40 min	Ordering	Put three objects in order from shortest to longest	Order by hand
40-52 min	One unit	Measure with clips: A is 5, B is 7	Measure and record
52-60 min	Exit check	Three questions collected and marked	Work independently

03 Teaching script (read it out)

Scene 1: Align the starting point before comparing

Length comparison has one starting rule: both left ends must touch the same line or table edge. With left ends together, whichever right end sticks out further is longer.
Why? If one pencil sits forward of the other, a further right end only means it was placed further along. The child does not have a sight problem; the idea of one shared ruler is missing. Before every comparison, make them say: my left ends are aligned.

Students do: press a pencil and a crayon to the same point on the table edge and say which right end sticks out.

Scene 2: Three wordings, and none may be skipped

There are only three results: longer than, shorter than, the same length. A pencil at 12 centimetres and a crayon at 15 centimetres means the pencil is shorter by 3 centimetres.
The same length is the one children skip. When two objects look close they say longer, even when both are 12 centimetres. Teach the same length first, then longer and shorter, so the answer is not treated as a two-way choice.

Students say: with two equal pencils aligned, state the same length and explain why it is not longer.

Scene 3: Measure with one unit so the counts can be compared

Without a ruler, use a non-standard unit: paper clips, squares, finger widths. The rule is that both objects use the same unit. Object A is 5 clips and object B is 7 clips, so B is longer by 2 clips.
The trap is measuring A with big clips and B with small ones; the numbers then mean nothing. Start at one end, place units end to end, with no gaps and no overlaps.

Students do: measure a textbook and a pencil case with clips, write both counts and say which is longer.

04 Question types and worked steps

Type	Example	Steps	Answer
Picture comparison	Which line is longer	Find the shared starting line first	Never judge by eye alone
Three wordings	Answer with longer than, shorter than or the same length	Give a full sentence	Name the object compared against
Ordering	Three objects from shortest to longest	Find the shortest, then the longest	Recheck the whole row
Non-standard unit	Measure with clips and compare	One unit, start at one end	Write the count and the unit

Sanity check (teach this): Sanity check: one end must be aligned or the result is void; 12 centimetres is shorter than 15 centimetres by 3; counts from different sized units cannot be compared; the same length is a valid answer, not a mistake.

05 Independent practice (3 questions)

Question	Answer	What to watch
Aligning	Align the left ends of three pairs	Both ends touch one line
Wordings	One sentence in each of the three forms	Each sentence names the other object
Ordering	Four pencils from shortest to longest	Shortest and longest correct
Measuring	Measure two objects with clips	The same clips used twice

06 Common mistakes and what to say

Mistake	Student writes	Say this
Comparing with both ends offset	The blue one is longer because it reaches further	Are the left ends touching the same line? Align them and say it again.
No object named	This one is long	Longer than what? Name the other object.
Mixing unit sizes	Big clips for A, small clips for B	Were the clips the same size both times? If not, the numbers cannot be compared.
Leaving gaps	A finger width between clips	The gaps mean part of the object was never measured. Do it again.

07 Homework (paper, section and question numbers)

Primary maths chapter index — All chapters by level
Teaching guide index — Same structure, other subjects
Redo this chapter — Questions 1 to 4 again, drawing the alignment line each time

08 Exit check (last 5 minutes)

Question	Answer	Decision
First move before comparing	Align one end to the same line	By eye alone means act one again
How many possible results	Three: longer, shorter, the same	Two means act two again
Same numbers from different sized clips	Not comparable; one unit is required	Yes means act three again

09 Tutor FAQ

Why not use a ruler straight away?

Primary 1 builds the idea of length with hands and objects; the ruler comes later. Given a ruler too early, children read numbers without knowing what the numbers measure.

Does the same length need teaching?

Yes. Children expect a two-way choice and force equal objects into longer, which later makes them accept sloppy measuring in centimetres.

How do you compare something curved?

Straighten it, or lay string along the shape and then measure the string. Direct comparison only works on objects that can be straightened.

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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.