Numbers up to 20
By the end of this lesson a child counts from 10 to 20 and sees that a number after 10 is one ten plus a few ones. Seventeen is not a new symbol. It is 10 and 7 more.
What the child can do at the end
- Say the numbers from 10 to 20 in order, without skipping 11, 12, or 15.
- For 16, say: one ten and 6 ones.
- Does not write 10 and 6 as 106.
How a number after 10 is built
Ten is two full hands, or one box of 10. The numbers 11 to 19 add ones onto that box. Twenty is two boxes of 10.
- 11 = 10 + 1
- 14 = 10 + 4
- 18 = 10 + 8
- 20 = 10 + 10
One problem, step by step
A box holds 10 pencils, and 6 more lie beside the box. How many pencils are there in all?
- The box is already 10. You do not count those pencils one by one.
- The loose pencils are added onto 10.
- Count six new ones from 10: 11, 12, 13, 14, 15, 16.
- The total is 16. That is 10 + 6, written as 16, not as 106.
A common mistake
The child sees 10 and 6 and writes 106. Ten and six join into one two-digit number. The first digit says how many tens there are, the second how many ones. One ten and six ones is 16.
The other mistake is the order after 10: the child says 10, 11, 13. After 11 comes 12, every time.
Practice
- What comes after 14?
- What is 10 + 3?
- What is 10 + 9?
- Which number is one ten and 0 ones, plus another ten?
- Say the numbers from 17 to 20.
Answers
- 15
- 13
- 19
- 20
- 17, 18, 19, 20
10 + 9 = 19. From 10, count nine more: 11, 12, 13, 14, 15, 16, 17, 18, 19.
After the lesson
When the child can say, without a pause, that 15 is 10 and 5, open the lesson on greater and smaller. Comparing numbers up to 20 starts by looking at the ten.
For a parent
Put ten matching objects in one bag and leave the rest outside. Let the child say “the bag and three more”, and only then the number 13.