Teaching with the 20 Tray
Teaches understanding of the teen numbers, adding 10 and 9 to a number, and ways of making 20.
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Building the 20-Stair
Children discover the role of 10 in each teen number as they build the stair from 1 to 20. They name the blocks in each step, such as 10 and 5, and then give their sum, 15. In this way they all understand the composition of each number from 11 to 20.
