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Confusion about teen numbers

Diagnostic questions

Ask the student to count from 7, stopping them when they reach 20.
Ask the student to count backwards from 23, stopping them when they reach 10.
Show the student the following teen numbers on a card and ask them what they are: 14, 12, 15, 17, 11.

What to notice in the student’s response

Can the student only count forwards to 12?
Does the student have difficulty distinguishing between “-ty” and “-teen” numbers, saying thirty instead of thirteen?
Does the student count out of sequence when counting forwards or backwards?
Is the student able to identify all the teen numbers?
Does the student mix up numbers such as 12 and 21?
Does the student count up from 1 to identify a number?

Deliberate acts of teaching


Many students are unaware that “x-teen” in English means “x” ones and one ten.

Focus on the language patterns of teen numbers.

1–20 number card sets
Ask the students to place the cards in order from 1–20, using a number strip as support if necessary. Move the numbers 11–20 beneath the row of numbers from 1–10, pointing out the number pattern. With the student, count forwards and backwards from different points through teen numbers, asking the student to identify each teen number and the numbers that come before and after it.

Number flip strip to 20
Show the students the numbers 11–20, then cover all but one number. Point to any hidden number and ask the student what number it is. Ask the student how they worked it out, encouraging them to count aloud.

Playground teen numbers
Use a painted number strip or hoops and laminated A4-sized teen numbers. Ask the student to physically count forwards and backwards along the number strip. Use different starting numbers to count on and back from. Ask the student to jump on the number before or after a specific teen number. Throw a bean bag onto a number and ask the student to say which number it has landed on. A similar activity can be completed inside, using a set of 1–20 cards and a number mat with teen numbers.

What to do next if the student is stuck

Use a large calendar with numbers 1 to 31. Place an iceblock stick in each square. As each number is counted, move the iceblock stick(s) from the preceding square into the next square. When 10 is reached, bundle the ten sticks together and move them as a bundle. When the sticks are moved to 11 the student will see 1 ten and 1 one. By the time the sticks reach 23, there will be 2 bundles of ten and 3 single sticks. Continue up to 31.

Initiating home-based activities

Send home a set of 1–20 number cards and a 1–20 number strip. The student can:

  • pick up five random numbers and place them in order of size
  • pick up a number and tell their parent which numbers come before and after
  • practise writing teen numbers
  • place the number cards in order and then turn them over.

The parent removes a number from the row and closes the gap, then asks the student to identify which number it is. The student turns over the rest of the cards to work this out.

Next teaching steps back in the classroom

Work on developing the student’s conceptual understanding of the place value of teen numbers, for example, 17 represents 1 ten and 7 ones.
Use Peter Hughes’ (Auckland University) “Read, Say, Do, Times Two” model. Students who can “read and say” the teen numbers also need to be able to “do” the teen numbers. For example, for 17, the student needs to be able to count out 17 items by counting from 1 to 17, and be able to show 17 as one bag of 10 lollies and 7 loose lollies. Other materials that can be used include bundles of sticks, tens frames, beans in canisters, an abacus, and arrow cards.