AC9M3N03
Official content description
add and subtract two- and three-digit numbers using place value to partition, rearrange and regroup numbers to assist in calculations without a calculator
What AC9M3N03 actually looks like when you teach it
The descriptor says without a calculator and it also, deliberately, doesn't say algorithm. The work is partitioning, rearranging and regrouping — mental and jotted methods built on place value. Split-and-add (300 + 40 + 2), jump strategies on an empty number line, compensating by rounding to a friendly number and adjusting back. Children who meet the vertical algorithm before these strategies tend to abandon reasoning for procedure, and then can't tell when their answer is nonsense. Keep the empty number line on the board all term.
What the class will get wrong — and what to do about it
The error
In subtraction, taking the smaller digit from the larger in each column regardless of position: 342 − 128 giving 226, because 8 − 2 was done instead of 2 − 8.
How to confront it
Estimate first, every time — 342 − 128 is roughly 340 − 130, so about 210. An answer of 226 fails its own estimate. Then rebuild the subtraction with MAB so the regrouping is a physical trade rather than a rule about crossing out.
Ready to put on the board
We are learning to add and subtract two- and three-digit numbers using place value.
- I can estimate the answer before I calculate.
- I can partition numbers to make the calculation easier.
- I can check whether my answer is reasonable.
Estimate, solve, check
- Write 456 − 187. Before anything else, everyone writes an estimate on their whiteboard and holds it up.
- Collect the estimates. They should cluster around 270 — discuss any that don't.
- Now solve it. Take two different methods and record both on the board, one as jumps on the empty number line.
- Compare each answer to the estimate. Does it survive?
- Repeat with 305 − 178, which forces regrouping across a zero. This is the one to spend time on.
Free to use in your classroom. Written for AC9M3N03, not adapted from another year level.
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The Year 3 Maths planning scaffold
A one-page planning sheet with the official achievement standard, every content description grouped by strand, and space for your assessment and week-by-week sequence. Print it and plan on paper, or use it as the skeleton for a unit.
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What Year 3 Maths students should achieve
Coverage is judged against the achievement standard — not by ticking every content description. These are the official Year 3 Maths standard sentences this code builds towards:
- Students conduct guided statistical investigations involving categorical and discrete numerical data, and interpret their results in terms of the context.
- They use mathematical modelling to solve practical problems involving single-digit multiplication and division, recalling multiplication facts for twos, threes, fours, fives and tens, and using a range of strategies.
- They create algorithms to investigate numbers and explore simple patterns.
- Students represent unit fractions and their multiples in different ways.
- Students use familiar metric units when estimating, comparing and measuring the attributes of objects and events.
- By the end of Year 3, students order and represent natural numbers beyond 10 000.
The Number progression either side of AC9M3N03
A class can only meet this descriptor if they were taught the one before it. If yours hasn't, that's where the lesson starts — not here.
Taught before · Year 2
- AC9M2N01recognise, represent and order numbers to at least 1000 using physical and virtual materials, numerals and number lines
- AC9M2N02partition, rearrange, regroup and rename two- and three-digit numbers using standard and non-standard groupings; recognise the role of a zero digit in place value notation
- AC9M2N03recognise and describe one-half as one of 2 equal parts of a whole and connect halves, quarters and eighths through repeated halving
Builds towards · Year 4
- AC9M4N01recognise and extend the application of place value to tenths and hundredths and use the conventions of decimal notation to name and represent decimals
- AC9M4N02explain and use the properties of odd and even numbers
- AC9M4N03find equivalent representations of fractions using related denominators and make connections between fractions and decimal notation
Other Year 3 Number codes
- AC9M3N01recognise, represent and order natural numbers using naming and writing conventions for numerals beyond 10 000
- AC9M3N02recognise and represent unit fractions including 1/2, 1/3, 1/4, 1/5 and 1/10 and their multiples in different ways; combine fractions with the same denominator to complete the whole
- AC9M3N04multiply and divide one- and two-digit numbers, representing problems using number sentences, diagrams and arrays, and using a variety of calculation strategies
- AC9M3N05estimate the quantity of objects in collections and make estimates when solving problems to determine the reasonableness of calculations
- AC9M3N06use mathematical modelling to solve practical problems involving additive and multiplicative situations including financial contexts; formulate problems using number sentences and choose calculation strategies, using digital tools where appropriate; interpret and communicate solutions in terms of the situation
- AC9M3N07follow and create algorithms involving a sequence of steps and decisions to investigate numbers; describe any emerging patterns
Content description and achievement standard © Australian Curriculum, Assessment and Reporting Authority (ACARA), Australian Curriculum Version 9, used under CC BY 4.0. TeachKoala is not affiliated with or endorsed by ACARA.