Teaching pack: Addition and Subtraction Undo Each Other (Year 3) -- a week of maths lessons

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Teaching pack · Year 3 Algebraseegongsik /au

Addition and Subtraction Undo Each Other: a week of ready-to-teach maths

Five days of lessons for Year 3 Algebra. Print this pack and the week is prepared: each day has a one-page plan and a student worksheet, plus cut-out cards, a mini-check and answers.

AC9M3A01

recognise and explain the connection between addition and subtraction as inverse operations, apply to partition numbers and find unknown values in number sentences

Start here: five minutes to Monday

Skim the week at a glance on the next page.
Print the five days (plan + worksheet each).
Cut out the card sheet once; reuse all week.
Open the free interactive unit on your board.
Teach from the plan: timings, talk prompts and answers are on one page.

No maths background needed

Written for the busy generalist teacher. Plain words, common muddles, and model answers are on every plan.

On the board

On-screen pictures for this unit include: “The fact family”, “Build and undo”, “Find the unknown”, “Check by inverse”, “Partition partner”. Each day plan names which picture to show.

seegongsik.com/au/y3/algebra/AC9M3A01

Aligned to the Australian Curriculum V9 (AC9M3A01). Original material from seegongsik, not endorsed by ACARA. Descriptors (c) ACARA, CC BY 4.0. Free to print and use in class.

The week at a glance5 lessons

The week at a glance

One lesson a day. Run them in order where you can.

Day	Lesson	Children learn and do	On screen
1	The fact family	Practise the idea with talk, board and worksheet	Board: The fact family
2	Build and undo	Practise the idea with talk, board and worksheet	Board: Build and undo
3	Find the unknown	Practise the idea with talk, board and worksheet	Board: Find the unknown
4	Check by inverse	Practise the idea with talk, board and worksheet	Board: Check by inverse
5	Partition partner	Practise the idea with talk, board and worksheet	Board: Partition partner

Materials (one trip)

This pack printed (plans, worksheets, cards, mini-check).
Pencils, scrap paper, and the board or projector for the interactive unit.
Optional counters, number cards or rulers if your day plan names them.

A note home

This week in maths we work on addition and subtraction undo each other. Ask: What did you practise today? Can you show me with a drawing?

seegongsik.com/au/y3/algebra/AC9M3A01/pack

Day 1 · Teacher planDay 1 of 5

The fact family

Children practise the idea behind “The fact family” using talk, the board picture, and a short worksheet. About 40 minutes.

We are learning to

explain the idea of the fact family in Year 3 words,
use the board picture to check our thinking,
record an example on paper.

Success criteria

I can show one example of today’s idea.
I can say the idea in a short sentence.

You need

interactive unit open on “The fact family”,
worksheet (next sheet), one per child,
optional cut-out cards from this pack.

Lesson flow (about 40 minutes)

5 min	Warm-up Quick oral examples linked to yesterday if any. Ask: “What do you already know that might help today?”
10 min	On the board Open “The fact family”. Press through the controls while children predict. Ask: “What changed on the screen? What stayed the same?”
15 min	Worksheet Children complete the day sheet. Circulate for muddles listed below.
10 min	Share Two children share an example. Class finishes the exit sentence. Ask: “In one sentence, what was today’s idea?”

On the board

Leave “The fact family” on screen for the main teaching block. Match button labels on the plan talk prompts to the live unit.

seegongsik.com/au/y3/algebra/AC9M3A01

Watch for

Skipping the board and only copying answers -- bring them back to the picture.
Correct answer with no explanation -- ask “how do you know?”.

Make it easier, make it bigger

Easier: do the first two worksheet items together.
Bigger: invent one new example for a partner to solve.

Answers and look-fors

Meeting the idea sounds like a clear sentence about the fact family.
Drawings or numbers match the board story, not random decoration.

Day 1 · Worksheet

The fact family

NameClassDate

Use the board picture. Show your thinking.

1. Draw or write one example from the board.

2. What is the main idea in your words?

3. Make a second example of your own.

I know I am right because

I can teach this idea to a partner:Yes □ No □

Day 2 · Teacher planDay 2 of 5

Build and undo

Children practise the idea behind “Build and undo” using talk, the board picture, and a short worksheet. About 40 minutes.

We are learning to

explain the idea of build and undo in Year 3 words,
use the board picture to check our thinking,
record an example on paper.

Success criteria

I can show one example of today’s idea.
I can say the idea in a short sentence.

You need

interactive unit open on “Build and undo”,
worksheet (next sheet), one per child,
optional cut-out cards from this pack.

Lesson flow (about 40 minutes)

5 min	Warm-up Quick oral examples linked to yesterday if any. Ask: “What do you already know that might help today?”
10 min	On the board Open “Build and undo”. Press through the controls while children predict. Ask: “What changed on the screen? What stayed the same?”
15 min	Worksheet Children complete the day sheet. Circulate for muddles listed below.
10 min	Share Two children share an example. Class finishes the exit sentence. Ask: “In one sentence, what was today’s idea?”

On the board

Leave “Build and undo” on screen for the main teaching block. Match button labels on the plan talk prompts to the live unit.

seegongsik.com/au/y3/algebra/AC9M3A01

Watch for

Skipping the board and only copying answers -- bring them back to the picture.
Correct answer with no explanation -- ask “how do you know?”.

Make it easier, make it bigger

Easier: do the first two worksheet items together.
Bigger: invent one new example for a partner to solve.

Answers and look-fors

Meeting the idea sounds like a clear sentence about build and undo.
Drawings or numbers match the board story, not random decoration.

Day 2 · Worksheet

Build and undo

NameClassDate

Use the board picture. Show your thinking.

1. Draw or write one example from the board.

2. What is the main idea in your words?

3. Make a second example of your own.

I know I am right because

I can teach this idea to a partner:Yes □ No □

Day 3 · Teacher planDay 3 of 5

Find the unknown

Children practise the idea behind “Find the unknown” using talk, the board picture, and a short worksheet. About 40 minutes.

We are learning to

explain the idea of find the unknown in Year 3 words,
use the board picture to check our thinking,
record an example on paper.

Success criteria

I can show one example of today’s idea.
I can say the idea in a short sentence.

You need

interactive unit open on “Find the unknown”,
worksheet (next sheet), one per child,
optional cut-out cards from this pack.

Lesson flow (about 40 minutes)

5 min	Warm-up Quick oral examples linked to yesterday if any. Ask: “What do you already know that might help today?”
10 min	On the board Open “Find the unknown”. Press through the controls while children predict. Ask: “What changed on the screen? What stayed the same?”
15 min	Worksheet Children complete the day sheet. Circulate for muddles listed below.
10 min	Share Two children share an example. Class finishes the exit sentence. Ask: “In one sentence, what was today’s idea?”

On the board

Leave “Find the unknown” on screen for the main teaching block. Match button labels on the plan talk prompts to the live unit.

seegongsik.com/au/y3/algebra/AC9M3A01

Watch for

Skipping the board and only copying answers -- bring them back to the picture.
Correct answer with no explanation -- ask “how do you know?”.

Make it easier, make it bigger

Easier: do the first two worksheet items together.
Bigger: invent one new example for a partner to solve.

Answers and look-fors

Meeting the idea sounds like a clear sentence about find the unknown.
Drawings or numbers match the board story, not random decoration.

Day 3 · Worksheet

Find the unknown

NameClassDate

Use the board picture. Show your thinking.

1. Draw or write one example from the board.

2. What is the main idea in your words?

3. Make a second example of your own.

I know I am right because

I can teach this idea to a partner:Yes □ No □

Day 4 · Teacher planDay 4 of 5

Check by inverse

Children practise the idea behind “Check by inverse” using talk, the board picture, and a short worksheet. About 40 minutes.

We are learning to

explain the idea of check by inverse in Year 3 words,
use the board picture to check our thinking,
record an example on paper.

Success criteria

I can show one example of today’s idea.
I can say the idea in a short sentence.

You need

interactive unit open on “Check by inverse”,
worksheet (next sheet), one per child,
optional cut-out cards from this pack.

Lesson flow (about 40 minutes)

5 min	Warm-up Quick oral examples linked to yesterday if any. Ask: “What do you already know that might help today?”
10 min	On the board Open “Check by inverse”. Press through the controls while children predict. Ask: “What changed on the screen? What stayed the same?”
15 min	Worksheet Children complete the day sheet. Circulate for muddles listed below.
10 min	Share Two children share an example. Class finishes the exit sentence. Ask: “In one sentence, what was today’s idea?”

On the board

Leave “Check by inverse” on screen for the main teaching block. Match button labels on the plan talk prompts to the live unit.

seegongsik.com/au/y3/algebra/AC9M3A01

Watch for

Skipping the board and only copying answers -- bring them back to the picture.
Correct answer with no explanation -- ask “how do you know?”.

Make it easier, make it bigger

Easier: do the first two worksheet items together.
Bigger: invent one new example for a partner to solve.

Answers and look-fors

Meeting the idea sounds like a clear sentence about check by inverse.
Drawings or numbers match the board story, not random decoration.

Day 4 · Worksheet

Check by inverse

NameClassDate

Use the board picture. Show your thinking.

1. Draw or write one example from the board.

2. What is the main idea in your words?

3. Make a second example of your own.

I know I am right because

I can teach this idea to a partner:Yes □ No □

Day 5 · Teacher planDay 5 of 5

Partition partner

Children practise the idea behind “Partition partner” using talk, the board picture, and a short worksheet. About 40 minutes.

We are learning to

explain the idea of partition partner in Year 3 words,
use the board picture to check our thinking,
record an example on paper.

Success criteria

I can show one example of today’s idea.
I can say the idea in a short sentence.

You need

interactive unit open on “Partition partner”,
worksheet (next sheet), one per child,
optional cut-out cards from this pack.

Lesson flow (about 40 minutes)

5 min	Warm-up Quick oral examples linked to yesterday if any. Ask: “What do you already know that might help today?”
10 min	On the board Open “Partition partner”. Press through the controls while children predict. Ask: “What changed on the screen? What stayed the same?”
15 min	Worksheet Children complete the day sheet. Circulate for muddles listed below.
10 min	Share Two children share an example. Class finishes the exit sentence. Ask: “In one sentence, what was today’s idea?”

On the board

Leave “Partition partner” on screen for the main teaching block. Match button labels on the plan talk prompts to the live unit.

seegongsik.com/au/y3/algebra/AC9M3A01

Watch for

Skipping the board and only copying answers -- bring them back to the picture.
Correct answer with no explanation -- ask “how do you know?”.

Make it easier, make it bigger

Easier: do the first two worksheet items together.
Bigger: invent one new example for a partner to solve.

Answers and look-fors

Meeting the idea sounds like a clear sentence about partition partner.
Drawings or numbers match the board story, not random decoration.

Day 5 · Worksheet

Partition partner

NameClassDate

Use the board picture. Show your thinking.

1. Draw or write one example from the board.

2. What is the main idea in your words?

3. Make a second example of your own.

I know I am right because

I can teach this idea to a partner:Yes □ No □

Cut-out cardsReuse all week

Talk cards for Addition and Subtraction Undo Each Other

Cut out. Hold up a card and give an example. Partner checks with the board if needed.

The fact family

Give an example.

Build and undo

Give an example.

Find the unknown

Give an example.

Check by inverse

Give an example.

Partition partner

Give an example.

Store in an envelope labelled AC9M3A01 for next year.

Mini-check · End of week

Show what you know: Addition and Subtraction Undo Each Other

NameClassDate

Work on your own. Use pictures or numbers.

1. Draw or write the big idea of this week.

2. Give one clear example.

3. Give a second different example.

4. What mistake should we watch for?

I can explain this idea to a partner:Yes □ No □

Mini-check · AnswersTeacher

Answers and look-fors

Item 1: names the unit idea (addition and subtraction undo each other) in child words.
Items 2-3: two different correct examples linked to the week’s pictures.
Item 4: a real muddle (wrong place value, unfair compare, mixed units, etc.).
At standard: clear example + short explanation. Beyond: teaches a partner with a new example.

Use day-plan look-fors across the week; this check is summative, not a surprise trap.

Descriptor: recognise and explain the connection between addition and subtraction as inverse operations, apply to partition numbers and find unknown values in number sentences