Year 1 - Maths
Crossing the tens boundary counting forwards and backwards
Pattern in counting from 20 to 100
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
In this unit pupils will extend their learning by counting to 100. They will explore the pattern in counting and focus on the end of the decade and the start of the new decade numbers. 
Lesson Summary
You will learn to count forwards and backwards within 100, crossing the tens boundary.
Key Notes
- The numbers from 0 to 100 have patterns that can help us to count forwards and backwards across the tens boundary.
- They are arranged differently on a number track and on a one hundred square.
- We can count the numbers in two ways.
- When a number ends in a 9, it is always followed by a decade number when counting in ones.
Vocabulary To Learn
- cross the tens boundary: The point at which the counting moves from one decade into another.
- forwards: When you count forwards the number become greater.
- backwards: When you count backwards the number become less.
Common Mistakes To Avoid
- Confusion around the numbers which cross the tens boundary, e.g. 39, 40 may say 39, 30
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
The numbers from 0 to 100 have patterns that can help us to count forwards and backwards across the tens boundary. They are arranged differently on a number track and on a one hundred square.
2. Use this key word in a maths sentence and explain it clearly. 'cross the tens boundary'
The point at which the counting moves from one decade into another. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Confusion around the numbers which cross the tens boundary, e.g. 39, 40 may say 39, 30. Correction: Make errors for the children to discuss; encourage them to explain and correct mistakes.
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