The note
How schools teach it now
Children sort using two rules at once. In a Venn diagram the overlap means 'both' and the space outside the circles means 'neither'. A Carroll diagram has rows and columns such as 'even / not even' and 'multiple of 3 / not a multiple of 3'.
5-minute kitchen-table activity
Make two overlapping circles with string on the table: 'red things' and 'round things'. Sort fruit, toys or cutlery into them. Where does a red apple go? A banana? A red pencil?
Worked example
A Venn diagram has two circles: 'even' and 'multiple of 3'. Where does 15 go?
- 15 is odd, so it is not in the 'even' circle.
- 15 = 3 × 5, so it is a multiple of 3.
- It goes in the 'multiple of 3' circle, but not in the overlap.
Answer: In 'multiple of 3' only
Common mistakes to watch for
- Putting something that fits both rules in only one circle.
- Forgetting the space outside both circles.
- Counting an item in the overlap twice when adding up.
Encouragement
- Try saying
- “Check each rule one at a time.”
- Rather than
- “It's just sorting, anyone can do it.”