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

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

Illustration for Watch and Notice Counting on is the route you already know. Today watch how partitioning and the near-double can be quicker. Before each jump is revealed, predict the landing number in your head.

46 + 7 by counting on

Watch the jumps. We start at 46 and hop forward 7 in ones to land on 53. These are small jumps, but there are a lot of them.

35 + 20 by one big jump

This time the second number is a tidy 20, so we make one jump of twenty straight to 55. That is far fewer steps than counting on.

28 + 27 by partitioning

Watch how we split the 27 into 20 and 7. First we jump 20 to reach 48, then we jump 7 more to land on 55.

24 + 25 as a near-double

These two numbers are almost the same. We use the double 24 + 24 = 48, then add one more to reach 49. A double we already know does most of the work.

Teacher Notes

Walk each example one at a time, pointing at the arcs as you narrate. Before each jump is revealed, pause and ask the class to predict the landing number, then confirm it together.

46 + 7 — count the seven ones aloud so pupils feel how many steps counting-on costs.
35 + 20 — contrast: one tidy jump beats seven small ones when the second number is a whole ten.
28 + 27 — emphasise jumping the tens first, then the units; this keeps the running total simple.
24 + 25 — ask 'what double is hiding here?' before revealing the +1.

The 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 — partition the 27 into 20 and 7.
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

This round is the practice bank — 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 — split the 28 into 20 and 8.
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?

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.

+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)

End of lesson

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Teacher Class Feed

1 - Getting Started ~4 mins

2 - Watch and Notice ~9 mins

46 + 7 by counting on

35 + 20 by one big jump

28 + 27 by partitioning

24 + 25 as a near-double

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

Coming up

Unlock the full learning experience

XP