When the students are fluent on the numbers from 1 through 19, I begin working on 20 through 29. Once they have learned that twenty stands for two tens, this goes quite quickly. Students with disabilities, however, often don't become fluent for quite some time after they clearly understand the concept. The fast oral practice is especially important for these students.
I have taught this using the counting sticks with place value folders and using just the counting chart. Neither way seems to be better overall than the other way. If you use the counting sticks, you have to keep going back and forth from the counting sticks to the written numbers, which is a problem for some students who can't easily go back and forth between tasks. If you use just the counting chart, you must have the students very adept at thinking about bundling and unbundling tens because they won't have the sticks to bundle and unbundle. Since I make sure my students are very adept at that, using just the counting chart seems quite easy to me. I then have them work with the counting sticks and place value charts as soon as they can name and write the numbers automatically.
Materials needed besides pencils and paper:
Display the counting chart. Tell the students you will be working on the numbers that come after 19. Then ask them to review the ones and tens by saying something like:
Let's look at the first row. We have all ones, don't we? We start with zero ones (point to each number as you describe it), then we have one one, then we have two ones, then three, then four, then five, six, seven, eight, and nine. Do we ever have enough to bundle in a ten? (“No.”)
Let's look at this row. (Point to the 10s row.) The next number after nine is ten. (Point.) Can we bundle ten ones? (“Yes.”)
Yes, we can bundle ten, so we have one ten and zero ones. How about eleven? What can we bundle in eleven? (“ten ones”)
We can bundle ten ones, so we have one ten and one one. In twelve we have one ten and two ones. In thirteen we have one ten and three ones. In each number in this row (pointing across the row), how many tens do we have? (“one”)
So, when we get to nineteen we have one ten and nine ones. If we add one more one, what do we have? Most students will say “one ten and ten ones,” though some will immediately say “two tens.”
If you have some students who say “one ten and ten ones” and some who say “two tens” (or if they all say “one ten and ten ones”) tell them that they are right, but in order to write it in the next space we have to bundle the ten ones, so we have two tens. Write in the 2. Ask how many ones are left over and write in the 0. If all the students say “two tens,” just write in the 2 and continue asking about the ones. To introduce the name, say something like:
Now we have two tens and zero ones. We call that twenty. Twen ty stands for two tens. We don't say anything for the zero ones, just like we only say ten for one ten and zero ones (point).
Write twen ty on the board and say two tens as you arc under the syllables of twen ty. Then arc again while you say twen ty.
Arc again while saying, If twen ty stands for two tens, which part stands for two? (“twen”)
Which part stands for tens? (“ty”)
I often say the same thing slowly a couple of times to give the students who process slowly more time to think. Write two and tens under the twen and ty to make it more apparent.
If someone comments on the similarity of the spelling or sound of twelve and twenty, reinforce their good observation; underline the twel and the twen and have the students say those parts of the words a couple of times. If no one comments on it, wait until you have finished introducing the 20s and then help them see the commonality in the names.
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