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# Cracking the 'teen number' code

Published almost 2 years ago by Ann Baker

Teen numbers have long been known to cause difficulties for young students.

This is in part due to the fact the English language explicitly show that numbers between 10 and 20 are made up of 10 and some more. This happens in larger numbers where, for example, we say thirty two and this shows that 32 is made of 30 and 2 more. In contrast, when we say fifteen it is far from clear that 15 is made of 10 and 5 more.

The irregularity in our counting sequence, with no pattern in 11, 12, 13, leads many children to say 40, 50, not hearing the ‘teen’ on the end.

Other languages make it clearer that eleven is 10 and 1 more. For example, the Mandarin for 15 is shi wu which separates the ten (shi) and the 5 (wu) and, in Mandarin, this convention holds for all the numbers from 11 to 19.

It’s our belief that when we say to a child that 13 is a 10 and three 1s, they don’t actually yet have the cognitive structures in their brain needed to understand what that means.

One of our books which can be used on the interactive whiteboard or printed to make a book, ‘Hidden Creatures’ shows that the numbers between 10 and 20 can be made in many ways using fun and engaging images.

About ‘Hidden Creatures’

The images in the book are created so that some of them build on from 10, with 10 creatures hidden and the ones shown, or in some instances the ones are hidden to further challenge students. For example, with the lady beetles, we’re trying to make clear visually that the teen numbers are easily built from 10 and some more. This also confirms that 10 is a friendly number as it ends in zero and is easy to add on to.

Hidden Creatures has been designed as a puzzle. Students look at the first page which poses a question such as ‘How many are missing?’. This enables them to build an understanding that 13 is made of 10 and 3 more. The second page reveals what was hidden and may have a sting in the tale such as ‘How many spots, legs, or stripes’, which means that there are opportunities to count in 2s, 5s and 10s as well.

Linking Natural Maths to the American and Australian Curriculum

The Common Core Standards in America emphasises 10s and 1s, the numbers between 11 and 19, and that students should know that teen numbers are composed of 10 and some more. The standards for mathematical practice in the CCS also state:

Quantitative reasoning entails habits of creating a coherent representation of the problem at hand. Considering the units involved, attending to the meaning of quantities not just how to compute them, and knowing and flexibly using different properties of operations and objects. (page 6)

The Australian Curriculum also says that students should be able to make correspondences between collections initially to 20 and explain their reasoning. It also says ‘look for and make use of structures’ – it’s these structures we’ve built into the ‘Hidden Creatures’ pictures.

Students’ reaction to ‘Hidden Creatures’

Teachers tell us that students absolutely love working out how many creatures are there and naming the strategies to find out how many are left. When the students have completed the problems, generally they want to go and make their own Hidden Creatures puzzle.

When you are using the book, allow time for the students to make their own page, as this is part of the reflection stage, which we encourage with all lessons.

Purchase 'Little Creatures' here today.

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