If you can look at a small collection of objects and see at a glance how many are there without counting, you can subitize!
But developing kids’ ability to see a collection of objects (or a number) as being made up of smaller ‘parts’ is something that traditionally has not been focused on in early maths. It’s important to do this, however, because it leads on to early understanding that ‘bits’ can be moved around from one number to another to make calculations much easier. Kids who begin developing this sort of flexible thinking about numbers from the very beginning of their schooling have a distinct advantage over the rest. Yet it is something that is frequently not taught!
So if you have a 4 or 5 year old, and you are busy teaching them to say the 0-9 number counting pattern to 10 or higher, and teaching them to count up to at least 6 objects (pointing to each object only once and not missing any out), now is the time to teach them to subitize and to think about number partitions.
How to start:
Get a 30cm x 20cm (approx) piece of cardboard or a box lid and five small objects, eg toy animals, pegs, pasta shells, counters. Sit on the floor facing your child, and say:
I’m going to show you some things for just a second and I want to see if you can tell me how many you see. There won’t be time to count, and this is not about counting. It’s about looking. First you need to close your eyes. When they’re closed, I’ll get ready.
Put one thing behind your cardboard barrier. Tell your child to open his eyes. Reveal the object behind your cardboard for just a second or two, and then hide it again.
How many teddies did you see?
How did you know it was one?
(Answer: I just knew.)
Repeat, but this time place two objects behind your barrier.
Ask the same questions:
How many teddies did you see?
How did you know it was two?
(Answer: I saw one and one, and so I knew it was two.)
Strongly encourage this type of response because the child has looked at the two in parts, and is therefore partitioning.
(Other likely answer: I just knew.) This answer is acceptable, but you should point out that you can also look at the two in parts, ie one and one. Note, this is NOT about teaching addition, it is about looking at a number in parts. You can practise using two objects of different colours to help make the partitioning clearer to your child. He’s more likely to say he saw one red one and one yellow one.
However, you don’t want your child to become dependent on using colour for partitioning, so you can vary your teaching by using two objects of different sizes. Your child is also likely to say he knew it was two because he saw one big one and one small one.
Eventually you want him to be able to say he saw one and one when the objects are exactly the same.
Repeat the process, with three objects.
Based on what you have previously done, you will probably find that here your child will say he knew it was three because he saw one and one and one. This is fine because it is partitioning. But it’s now time to point out that with three objects, sometimes you can see two objects and one object. You will need to demonstrate a few times using different objects grouped in different arrangements.
Work on subitizing 1, 2 and 3 until you see that your child has a great understanding and can give you the ‘right sort of answers’ to the two questions.
Then move on to subitizing with four objects.
Repeat the same process, using a variety of objects and remembering that you will need to point out the different partitions over time, saying:
I saw two and two that time!
I saw three, and one over there that time!
I saw one and three that time!
Work on subitizing 1, 2, 3 & 4. Look around for opportunities to subitise when you’re out and about (eg pictures on posters that you can cover with your hand) or playing a game with involving dice.
Children learn to recognise the numbers on a die very easily. They just know, for example, that a six is a six without needing to count the dots. Take the opportunity to point out that you can look at a six on a die as three and three, or as two and two and two. Don’t be tempted to teach subitizing with just a die, as you want your child to see partitions in all situations, and standard dice always use the same dot arrangements.
Remember that subitizing is ‘seeing at a glance’ and you show the objects for no more than a second or two so there is no time for counting. The word ”subitize’ comes from the Latin word ‘subitus’, meaning ‘sudden’.