The child uses a range of non-count by one strategies:
Compensation
Using known results
Adding to ten
Commutativity
Subtraction as the inverse of addition
Awareness of ten as a teen number
The Child Who Has Facile Number Structures to 20
This child has facile number structures to 20.
He can recall a large number of number facts within 20. He uses this knowledge and his experience of structuring numbers to quickly calculate any number problem within 20.