Year 1 - Maths
Crossing the tens boundary counting 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 backwards within 100, crossing the tens boundary.
Key Notes
- The numbers from 0 to 100 have patterns that can help us to count backwards across the tens boundary.
Vocabulary To Learn
- 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.
Common Mistakes To Avoid
- Confusion regarding the number before the decade numbers, e.g. saying 30, 39
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 backwards across the tens boundary. The numbers from 0 to 100 have patterns that can help us to count backwards across the tens boundary.
2. Use this key word in a maths sentence and explain it clearly. 'tens boundary'
This is where the pattern of counting changes at the start of the number to show a new decade has started. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Confusion regarding the number before the decade numbers, e.g. saying 30, 39. Correction: Explicitly look at the patterns in numbers that precede a decade number and discuss errors.
More Lessons In This Unit
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