New
New
Year 1

# Crossing the tens boundary counting backwards

I can count backwards within 100, crossing the tens boundary.

New
New
Year 1

# Crossing the tens boundary counting backwards

I can count backwards within 100, crossing the tens boundary.

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## Lesson details

### Key learning points

1. The numbers from 0 to 100 have patterns that can help us to count backwards across the tens boundary.

### Common misconception

Confusion regarding the number before the decade numbers, e.g. saying 30, 39

Explicitly look at the patterns in numbers that precede a decade number and discuss errors.

### Keywords

• Tens boundary - This is where the pattern of counting changes at the start of the number to show a new decade has started.

• Cross the tens boundary - The point at which the counting moves from one decade into another.

• Decade number - This is a multiple of ten which mark the tens boundary where the pattern of counting changes.

Give daily opportunities for counting both forwards and backwards up to 100 and within 100 from different starting points.
Teacher tip

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Starter quiz

### 6 Questions

Q1.
On a one hundred square, a number ending in a 9 is always followed by a __________.
ten
Q2.
Match each decade number to the end of the correct row of the one hundred square.

100

30

50

Q3.
Sort these numbers in the order you would say them when counting forwards.
1 - 39
2 - 40
3 - 41
4 - 42
Q4.
Sort these numbers in the order you would say them when counting backwards.
1 - 43
2 - 42
3 - 41
4 - 40
Q5.
Aisha is counting forwards. She is saying how many tens each number has. After 6 tens 9, what will she say?
6 tens 10
6 tens 8
Q6.
Which one of these counting sequences is not correct when counting backwards.
49, 48, 47
32, 31, 30

## Exit quiz

### 6 Questions

Q1.
Which row on the one hundred square is before the thirties?
the forties
the fifties
Q2.
The pattern of counting changes when you __________.
Correct answer: cross the tens boundary
Q3.
Match each decade number to the correct number that comes before it.

49

59

69

Q4.
Sort these numbers in the order you would say them when counting backwards.
1 - 52
2 - 51
3 - 50
4 - 49
Q5.
Aisha is counting backwards from the decade number 40. Which numbers will she say next?