In a nutshell
Decomposition is the ability to break a whole number into smaller parts in different ways.
In decomposition tasks, students are shown a whole amount, one visible part, and one hidden or missing part. Students work out the missing part using understanding of part-part-whole relationships.
In Foundation, decomposition tasks often involve small quantities using blocks, counters, fingers, dot patterns, five-frames, ten-frames, or part-part-whole mats alongside numerals. Students first solve smaller decomposition tasks within 5 before progressing towards larger quantities within 10.
As students develop, they increasingly recognise small number combinations automatically and rely less on counting-by-ones. For example, they may know that 5 can be 2 and 3, 4 and 1, or 5 and 0.
Decomposition supports later addition and subtraction because students learn that numbers are made of parts and wholes. This understanding helps them solve missing-part problems, understand fact families, and use known number combinations flexibly.
As students move into Year 1, decomposition skills are increasingly represented through addition and subtraction number facts.
This guidance is designed for classes where ENSSA results indicate a class-wide need to strengthen part-part-whole understanding and missing-part reasoning.
See also: Addition and Subtraction
Teaching guidance
06Resources for all teachers (Tier 1)View resourceHide resource↓
For schools and teachers using Ochre curriculum materials
Choose the curriculum used by your school, then find the relevant Foundation or Year 1 resource.
Make sure you’re logged into Ochre first, then open the resource link.
This section is for teachers using Ochre units as part of Tier 1 mathematics instruction in Victorian Curriculum settings, including MACS and CESL schools.
Use Ochre unit lessons when students need teaching or reteaching. Use Ochre Daily Review when students have already been taught the skill and need practice, reactivation or fluency-building.
Step 1: Where does this sit in your teaching sequence?
The skill has not yet been taught and is coming up soon
Let the scheduled Ochre lesson address it. Consider brief pre-teaching for students flagged by ENSSA.
The skill has not yet been taught and is scheduled much later this year
Consider bringing the relevant lesson section forward for flagged students only — check prerequisite lessons first.
The skill has already been taught
Go to Step 2 below.
The skill was taught a while ago, last term or last year
Start with Daily Review as a quick reactivation and accuracy check. If students are still inaccurate, go to Step 2.
Step 2: How are students performing right now?
Use this once you’ve confirmed the skill has already been taught.
Students are inaccurate or unsure
Use the Ochre unit lesson section first — not Daily Review.
Most students are inaccurate
Reteach the relevant modelling/guided-practice section to the whole class.
A few students are inaccurate but most are secure
Use the lesson section for small-group reteaching with flagged students only.
Students are accurate but slow or inconsistent
Use Daily Review — do not run a full reteach.
Has this skill been introduced?
This only asks about timing. Whether the class is accurate is something Daily Review over the next few days will show; it does not need to be judged in advance.
Yes
Use the Daily Review resource below, every day, for an initial five consecutive instructional days, regardless of how accurate the class is assumed to be.
No, but it is coming soon
Do not start Daily Review yet. Read the background sections (Teaching guidance; Vocabulary, representations and stem sentences) and preview the unit lesson below now, ahead of when it is scheduled.
No, and it is not scheduled soon
Check curriculum sequencing and prerequisite knowledge. Consider brief, targeted pre-teaching for the students ENSSA flagged, not a full classwide response ahead of schedule.
After five days of Daily Review
One brief daily note is enough: accuracy, independence and efficiency, not a per-student written record.
Clear improvement, not yet secure
Continue the same Daily Review resource.
Most accurate and increasingly efficient
Continue Daily Review as ongoing cumulative practice; no full reteach is needed.
Most students remain inaccurate or dependent on support
Use the unit lesson section to teach it explicitly, not Daily Review.
Most students are secure, but the same smaller group persists
Keep whole-class Daily Review; use the unit lesson materials with that group specifically.
Foundation
Build foundations for this skill.
FN02V Part-wholeUse this when students are inaccurate or unsure with parts and wholes, partitioning, missing parts, or recognising combinations.
FN02V Part-whole
This is the primary Foundation Ochre resource for decomposition. Teaches partitioning numbers to 5 and 10 into two and three parts, identifying parts and whole, subitising parts, five-/ten-frame combinations, ‘how many more’ prompts, number pairs to 5 and 10, and making 10 from smaller parts.
Use the lesson matching the specific gap — partitioning, identifying parts/whole, subitising parts, five-/ten-frame combinations, ‘how many more,’ or number pairs.
- If students confuse the part and the whole → use identifying parts/whole sections.
- If students count every item each time → use subitising and frame-based sections.
- If students cannot find missing parts → use ‘how many more’ and number pair sections.
Number–Addition and Subtraction Daily Review deck, Part-whole slidesUse this when students have already had explicit part-whole teaching and need practice or reactivation.
Daily Review Topic Deck: Number – Addition and Subtraction, Part-whole section
Mirrors FN02V — partitioning to 5/10, combinations, subitising parts, frame-based parts and ‘how many more.’
Do not use when students are not yet accurate identifying the whole and parts — return to FN02V lesson sections first.
FN04V Addition and SubtractionUse this when students are secure with decomposition and ready to apply part-whole knowledge to addition and subtraction contexts.
FN04V Addition and Subtraction
Follow-on unit that applies part-whole understanding to number stories, take-away situations and difference on a number track.
Students need initial teaching of decomposition — use FN02V first.
Year 1
Extend this skill through Year 1.
Number–Addition and Subtraction Daily Review deck, Part-whole slidesUse this when students have already had explicit part-whole teaching and need practice or reactivation.
Daily Review Topic Deck: Number – Addition and Subtraction, Part-whole section
Mirrors FN02V — partitioning to 5/10, combinations, subitising parts, frame-based parts and ‘how many more.’
Do not use when students are not yet accurate identifying the whole and parts — return to FN02V lesson sections first.
This section is for teachers using Ochre units as part of Tier 1 mathematics instruction in WA Curriculum v9.0 settings. WA Curriculum calls Foundation year “Pre-Primary.”
Ochre does not yet publish a separate WA-specific resource library. WA unit codes (PPN01W, 1N02W, and so on) map directly to the equivalent Australian Curriculum unit, so the buttons on these cards open the same Foundation and Year 1 Ochre pages as the Australian Curriculum tab.
Use Ochre unit lessons when students need teaching or reteaching. Use Ochre Daily Review when students have already been taught the skill and need practice, reactivation or fluency-building.
Step 1: Where does this sit in your teaching sequence?
The skill has not yet been taught and is coming up soon
Let the scheduled Ochre lesson address it. Consider brief pre-teaching for students flagged by ENSSA.
The skill has not yet been taught and is scheduled much later this year
Consider bringing the relevant lesson section forward for flagged students only — check prerequisite lessons first.
The skill has already been taught
Go to Step 2 below.
The skill was taught a while ago, last term or last year
Start with Daily Review as a quick reactivation and accuracy check. If students are still inaccurate, go to Step 2.
Step 2: How are students performing right now?
Use this once you’ve confirmed the skill has already been taught.
Students are inaccurate or unsure
Use the Ochre unit lesson section first — not Daily Review.
Most students are inaccurate
Reteach the relevant modelling/guided-practice section to the whole class.
A few students are inaccurate but most are secure
Use the lesson section for small-group reteaching with flagged students only.
Students are accurate but slow or inconsistent
Use Daily Review — do not run a full reteach.
Has this skill been introduced?
This only asks about timing. Whether the class is accurate is something Daily Review over the next few days will show; it does not need to be judged in advance.
Yes
Use the Daily Review resource below, every day, for an initial five consecutive instructional days, regardless of how accurate the class is assumed to be.
No, but it is coming soon
Do not start Daily Review yet. Read the background sections (Teaching guidance; Vocabulary, representations and stem sentences) and preview the unit lesson below now, ahead of when it is scheduled.
No, and it is not scheduled soon
Check curriculum sequencing and prerequisite knowledge. Consider brief, targeted pre-teaching for the students ENSSA flagged, not a full classwide response ahead of schedule.
After five days of Daily Review
One brief daily note is enough: accuracy, independence and efficiency, not a per-student written record.
Clear improvement, not yet secure
Continue the same Daily Review resource.
Most accurate and increasingly efficient
Continue Daily Review as ongoing cumulative practice; no full reteach is needed.
Most students remain inaccurate or dependent on support
Use the unit lesson section to teach it explicitly, not Daily Review.
Most students are secure, but the same smaller group persists
Keep whole-class Daily Review; use the unit lesson materials with that group specifically.
Foundation
Build foundations for this skill.
PPN02W Part-wholeUse this when students are inaccurate or unsure with parts and wholes, partitioning, missing parts, or recognising combinations.
PPN02W Part-whole (links to the Australian Curriculum unit FN02A in Ochre)
This is the primary Pre-Primary Ochre resource for decomposition. Teaches partitioning numbers to 5 and 10 into two and three parts, identifying parts and whole, subitising parts, five-/ten-frame combinations, ‘how many more’ prompts, number pairs to 5 and 10, and making 10 from smaller parts.
Use the lesson matching the specific gap — partitioning, identifying parts/whole, subitising parts, five-/ten-frame combinations, ‘how many more,’ or number pairs.
- If students confuse the part and the whole → use identifying parts/whole sections.
- If students count every item each time → use subitising and frame-based sections.
- If students cannot find missing parts → use ‘how many more’ and number pair sections.
Number–Addition and Subtraction Daily Review deck, Part-whole slidesUse this when students have already had explicit part-whole teaching and need practice or reactivation.
Daily Review Topic Deck: Number – Addition and Subtraction, Part-whole section
Mirrors PPN02W — partitioning to 5/10, combinations, subitising parts, frame-based parts and ‘how many more.’
Do not use when students are not yet accurate identifying the whole and parts — return to PPN02W lesson sections first.
PPN04W Addition and SubtractionUse this when students are secure with decomposition and ready to apply part-whole knowledge to addition and subtraction contexts.
PPN04W Addition and Subtraction (links to the Australian Curriculum unit FN04A in Ochre)
Follow-on unit that applies part-whole understanding to number stories, take-away situations and difference on a number track.
Lessons 1–12: pictorial and materials-based addition stories (1–4), pictorial and materials-based subtraction/take-away stories (5–8), and difference on a number track (9–12).
Students need initial teaching of decomposition — use PPN02W first.
Year 1
Extend this skill through Year 1.
Number–Addition and Subtraction Daily Review deck, Part-whole slidesUse this when students have already had explicit part-whole teaching and need practice or reactivation.
Daily Review Topic Deck: Number – Addition and Subtraction, Part-whole section
Mirrors PPN02W — partitioning to 5/10, combinations, subitising parts, frame-based parts and ‘how many more.’
Do not use when students are not yet accurate identifying the whole and parts — return to PPN02W lesson sections first.
This section is for teachers using Ochre units as part of Tier 1 mathematics instruction in Australian Curriculum v9.0 settings.
Use Ochre unit lessons when students need teaching or reteaching. Use Ochre Daily Review when students have already been taught the skill and need practice, reactivation or fluency-building.
Step 1: Where does this sit in your teaching sequence?
The skill has not yet been taught and is coming up soon
Let the scheduled Ochre lesson address it. Consider brief pre-teaching for students flagged by ENSSA.
The skill has not yet been taught and is scheduled much later this year
Consider bringing the relevant lesson section forward for flagged students only — check prerequisite lessons first.
The skill has already been taught
Go to Step 2 below.
The skill was taught a while ago, last term or last year
Start with Daily Review as a quick reactivation and accuracy check. If students are still inaccurate, go to Step 2.
Step 2: How are students performing right now?
Use this once you’ve confirmed the skill has already been taught.
Students are inaccurate or unsure
Use the Ochre unit lesson section first — not Daily Review.
Most students are inaccurate
Reteach the relevant modelling/guided-practice section to the whole class.
A few students are inaccurate but most are secure
Use the lesson section for small-group reteaching with flagged students only.
Students are accurate but slow or inconsistent
Use Daily Review — do not run a full reteach.
Has this skill been introduced?
This only asks about timing. Whether the class is accurate is something Daily Review over the next few days will show; it does not need to be judged in advance.
Yes
Use the Daily Review resource below, every day, for an initial five consecutive instructional days, regardless of how accurate the class is assumed to be.
No, but it is coming soon
Do not start Daily Review yet. Read the background sections (Teaching guidance; Vocabulary, representations and stem sentences) and preview the unit lesson below now, ahead of when it is scheduled.
No, and it is not scheduled soon
Check curriculum sequencing and prerequisite knowledge. Consider brief, targeted pre-teaching for the students ENSSA flagged, not a full classwide response ahead of schedule.
After five days of Daily Review
One brief daily note is enough: accuracy, independence and efficiency, not a per-student written record.
Clear improvement, not yet secure
Continue the same Daily Review resource.
Most accurate and increasingly efficient
Continue Daily Review as ongoing cumulative practice; no full reteach is needed.
Most students remain inaccurate or dependent on support
Use the unit lesson section to teach it explicitly, not Daily Review.
Most students are secure, but the same smaller group persists
Keep whole-class Daily Review; use the unit lesson materials with that group specifically.
Foundation
Build foundations for this skill.
FN02A Part-wholeUse this when students are inaccurate or unsure with parts and wholes, partitioning, missing parts, or recognising combinations.
FN02A Part-whole
This is the primary Foundation Ochre resource for decomposition. Teaches partitioning numbers to 5 and 10 into two and three parts, identifying parts and whole, subitising parts, five-/ten-frame combinations, ‘how many more’ prompts, number pairs to 5 and 10, and making 10 from smaller parts.
Use the lesson matching the specific gap — partitioning, identifying parts/whole, subitising parts, five-/ten-frame combinations, ‘how many more,’ or number pairs.
- If students confuse the part and the whole → use identifying parts/whole sections.
- If students count every item each time → use subitising and frame-based sections.
- If students cannot find missing parts → use ‘how many more’ and number pair sections.
Number–Addition and Subtraction Daily Review deck, Part-whole slidesUse this when students have already had explicit part-whole teaching and need practice or reactivation.
Daily Review Topic Deck: Number – Addition and Subtraction, Part-whole section
Mirrors FN02A — partitioning to 5/10, combinations, subitising parts, frame-based parts and ‘how many more.’
Do not use when students are not yet accurate identifying the whole and parts — return to FN02A lesson sections first.
FN04A Addition and SubtractionUse this when students are secure with decomposition and ready to apply part-whole knowledge to addition and subtraction contexts.
FN04A Addition and Subtraction
Follow-on unit that applies part-whole understanding to number stories, take-away situations and difference on a number track.
Lessons 1–12: pictorial and materials-based addition stories (1–4), pictorial and materials-based subtraction/take-away stories (5–8), and difference on a number track (9–12).
Students need initial teaching of decomposition — use FN02A first.
Year 1
Extend this skill through Year 1.
Number–Addition and Subtraction Daily Review deck, Part-whole slidesUse this when students have already had explicit part-whole teaching and need practice or reactivation.
Daily Review Topic Deck: Number – Addition and Subtraction, Part-whole section
Mirrors FN02A — partitioning to 5/10, combinations, subitising parts, frame-based parts and ‘how many more.’
Do not use when students are not yet accurate identifying the whole and parts — return to FN02A lesson sections first.
Intervention resources (Tier 2 & Tier 3)
Targeted supports for students or small groups when classwide teaching is not enough.
Intervention resources
The Ochre Intervention Modules are Tier 2/3 resources, built on the same Foundation–Year 2 Ochre content already used for Tier 1, for students who need more than classwide or targeted small-group support.
Part-wholeLessons 1–8, 15–19 · numbers 0–20
Covers partitioning a whole into parts and recording with number bonds. The same module continues directly into Addition and Subtraction Facts; a student needing this is often ready to move through both in sequence.
Small-group or 1:1, outside the classroom, by a teacher, learning assistant or trained volunteer; approximately 20 minutes per lesson.
Scripted lesson plans, a slide deck per lesson, a student workbook, assessment checkpoints, and explainer or demonstration videos.
This is a Tier 2/3 escalation, not a first response to an ENSSA flag. Use it once targeted small-group support from the Ochre resources has not resolved the gap.
Assessment checkpoints sit at the end of each sequence and indicate whether a student is ready to return to Tier 1 instruction alone.