Teen versus Ty numbers

If you’re a primary teacher, you’ll know what I’m talking about!! Teen numbers are those ending in teen. They are often confused with -ty numbers such as twenty, thirty, etc.


Oliver is pretty proud of the fact that he can count to 110 and beyond (we stopped him in the interest of time!)! However, we’d begun to notice that he often confuses his teen numbers (13 – 19) with his -ty numbers (20, 30, 40 etc.). Once we realized this, the first thing I needed to identify was the cause. There were 3 possibilities:

Identifying the Cause

  1. ls it a problem understanding quantity (number sense)?
  2. Is it a problem understanding the language (word form)?
  3. Or is it a problem understanding the symbols (standard form)?

To find out which one was affecting Oliver, I had to assess each one. To check for number sense, I started with numbers that didn’t have those suffixes. I asked him to show me numbers such as 12 and 43 on an abacus or using base 10 blocks. I gave the instructions verbally (to check for language) and in standard form (to check his understanding of symbols). Then I repeated the task with -ty and -teen numbers. This helped me realize that he does have a good understanding of number sense.

Next, I gave him the numbers in standard form and asked him to order them. He was able to do that symbolically. When I asked him to point to 30 however; he wasn’t sure whether he should point to 13 or 30. This meant Oliver couldn’t differentiate between -teen numbers and -ty numbers based primarily on language.

The Problem with the English Language

The reason for this can be attributed to our meaningless vocabulary, lack of patterns in the vocabulary (eleven, twelve, thirteen?!) and no reference to place value, all of which is available in some other languages. If we spoke Chinese for instance, we wouldn’t have these difficulties because their language emphasizes the place value. Eleven is represented and said as ‘ten-one’, twelve is ‘ten-two’, etc. But alas, Oliver doesn’t speak Chinese.

So as any good Mom-teacher-mathematician would do, I started to look for ways to help him! Most of what I found was geared towards ESL learners or older students who could read. “Emphasize the endings. Enunciate your words!” These techniques haven’t seemed to work on my English-speaking kindergarten kid who can’t read very well. So what else could I try?

Some techniques to try

Van de Walle’s advice?

  “Almost always use base-ten models while teaching oral names”.

My advice?

Do that and follow it with explicit instruction, lots of practice and building language skills. Below are some of the best tasks I found for doing that.  Here is a video of us tackling some of these tasks.

  1. Sorting activity: Oliver sorted the numbers into two piles (-ty or -teen) and then we asked what is the same and what is different? We looked for patterns and noticed that -teen numbers all start with 1 and -ty numbers all end in zero.
  2. Make a match: In this game, I say the name of a number and Oliver has to find it in his deck to make a match.
  3. 100 chart bingo:  In this game, students place their disks on 10 numbers. The first one to remove them all wins. 
  4. Listening tasks: have students concentrate on different sounds and build the numbers with base 10 blocks or an abacus.

Well, it doesn’t look like either piece of advice worked in the short term! However, when I reassessed Oliver a few months later, his language and reading had improved and as a result, so had his understanding of -ty and -teen numbers.

The bottom-line

I often say to my Kindie friends, that spending time learning how to read and write the numbers is not a math skill; it is a literary skill. Differentiating -teen and -ty is also a language skill. That being said, knowing how to read and write numbers is extremely important. Children who can read and write numbers are representing them symbolically and without that understanding, mathematics would be very time-consuming! Imagine solving 423 + 124 if you didn’t have symbols to represent that quantity?!

Just remember to balance your instructional time. If you are working on writing numbers, you are not working on number sense, so make sure you have time in the week to do both. Want more advice on teaching numbers? See my earlier post on Digits versus Numbers. Have more suggestions on how to help kids learn the difference between -ty and =teen? Please share them in the comment section!

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