Mental Addition Strategies Within 100

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1 Getting Started
2 Watch and Notice
3 Try It Together
4 Show Your Strategy in Your Copy
5 Class Challenge
6 What Did We Notice?
7 What's Next
Pupil practice

1 - Getting Started ~4 mins

Illustration for Getting Started A team has 32 points and scores 9 more. Roughly, what is their new total? You already know how to count on in ones, so think about how you would get there. Would you count on nine ones from 32, or is there a faster route hiding in those numbers?

Key point

Counting on is our familiar route from before. Today we add two brand-new routes that can be even faster, and we pick the one that saves us the most steps.

Teacher Notes

Pose 32 + 9 and take two or three hands-up routes, not open call-outs. Listen for 'count on' versus 'add ten, take one back'. Revoice both as valid — the point is that smart adders choose a route, they don't always count in ones.

👇 Mark your steps as done as you complete them.

+5 XP

2 - Watch and Notice ~9 mins

The number line will show four additions, each jumped a different way. Counting on is the route you already know, so watch how a big jump, partitioning and a near-double can be quicker. Before each jump is revealed, predict the landing number in your head.

Teacher Notes

Point at the arcs as each one appears. Ask for a prediction before revealing each jump, then confirm together.

46 + 7 counting on: start 46, seven single hops to 53. Count the ones aloud so they feel how many steps it costs.

35 + 20 one big jump: second number is a whole ten, so one jump of 20 to 55. Contrast with the seven small hops.

45 + 27 partitioning: split 27 into 20 and 7, jump 20 to 65, then 7 to 72. Tens first keeps the running total simple.

24 + 25 near-double: ask what double is hiding here before the reveal. Double 24 + 24 = 48, then one more to 49.

Big idea: the numbers tell you which route is fastest.

👇 Mark your steps as done as you complete them.

+10 XP

3 - Try It Together ~9 mins

Today we work through these additions together on the number line: 33 + 8, 42 + 30, 26 + 27, and 23 + 24. One pupil works at the board for each addition while the rest of the class follows along and predicts the landing number before it is confirmed. For each one, we choose a route first, then draw the jumps to land on the total.

Choose a route and jump

Teacher Notes

This round is for talking it through together — one pupil works at the board for each addition and the class agrees or corrects out loud.

Before each addition, ask the class which route they would pick and why. Let the pupil at the board draw their chosen jumps; the rest predict the landing number before it is confirmed.

33 + 8 — counting on is fine here, but watch for a pupil who bridges through 40 (+7 then +1).
42 + 30 — one jump of thirty; reward the pupil who resists counting in tens three times.
26 + 27 — near-double: double 26 is 52, then one more.
23 + 24 — near-double: double 23 is 46, then one more.

+15 XP

4 - Show Your Strategy in Your Copy ~3 mins

COPYBOOK MOMENT

In your maths copy, show your strategy for these two additions. Beside each one, draw a quick jotting on a number line: a jump for counting on, a split for partitioning, or a near-double if the numbers are close.

33 + 8
26 + 27

Teacher Notes

Walk the room glancing at the jottings — is the route sensible for the numbers? This is whole-class copybook practice, not marking. Look for pupils still counting in ones when a tidier route is sitting there.

+10 XP

5 - Class Challenge ~8 mins

A scoreboard is adding up totals: 43 + 6, 38 + 20, 27 + 28, and 49 + 49. We work through these together at the board. For each one, choose the route that saves the most steps, then draw the jumps and check.

Add it with the smartest route

Teacher Notes

These are the practice questions — pupils take turns at the board, check each answer, and the class confirms before moving on. Keep the board work brisk rather than over-explaining.

43 + 6 — small jump, counting on; quick win for a less confident pupil.
38 + 20 — resist counting in tens twice; one jump of twenty.
27 + 28 — near-double: double 27 is 54, then one more.
49 + 49 — the near-double: double 49 is 98, no adjustment needed. Ask 'which short cut saves the most steps here?' as each one is solved.

+15 XP

6 - What Did We Notice? ~2 mins

MATHS TALK

When does counting on in ones become the slow way, and a partition or a near-double the smart way? For which of today's additions would counting on in ones be the slow way?

Now look at a new pair: 36 + 28. Are these two close numbers? No, so a near-double is not the smart route. The second number has tens and units, so we partition: jump 20 from 36 to 56, then jump 8 to land on 64. Compare that with today's near-doubles like 27 + 28, where the numbers sit side by side.

So: a big tidy number wants one jump; two close numbers want a near-double; tens and units that are not close want a partition.

Teacher Notes

Listen for pupils naming the size of the second number as the clue, a big tidy number wants one jump, two close numbers want a near-double. Revoice a strong answer: 'so the numbers themselves tell you which route is fastest.' Head off the idea that counting on is always wrong, it is perfectly smart for 43 + 6.

Work 36 + 28 on the board to show partition when the numbers are not close:

Ask: are 36 and 28 close enough for a near-double? (No, they differ by 8.)
Partition 28 into 20 + 8.
Jump 36 → 56 (+20), then 56 → 64 (+8).

Slip to watch: pupils calling every two-part jump a near-double. Contrast with 27 + 28 from earlier so they feel the difference.

+10 XP

7 - What's Next ~3 mins

What we learned today

Good adders pick a smart route: count on, partition into tens and units, or lean on a near-double.
The jumps on a number line show the route clearly.
Big tidy numbers want one jump; two close numbers want a near-double.

Coming up

Next we turn this thinking around and look at smart ways to subtract within 100: counting back, and counting up to find the gap.

Teacher Notes

Close briefly. Reassure pupils that there is no single 'right' route — the skill is choosing one that fits the numbers in front of them.

+5 XP

Pupil practice

Module 2 · The Four Operations: Mental and Written Number

Lesson 13 · Mental Addition Strategies Within 100

Download Activity Book page (PDF)

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Teacher Class Feed

1 - Getting Started ~4 mins

2 - Watch and Notice ~9 mins

3 - Try It Together ~9 mins

Choose a route and jump

4 - Show Your Strategy in Your Copy ~3 mins

5 - Class Challenge ~8 mins

Add it with the smartest route

6 - What Did We Notice? ~2 mins

7 - What's Next ~3 mins

What we learned today

Unlock the full learning experience

XP