Subitizing

Definition:
Original meaning = "instantly seeing how many" (Clements, 1999, p. 400)

Two types of subitizing:

1. Perceptual – “Recognising a number without using other mathematical processes” (Clements, 1999, p.401)

2. Conceptual – Recognising number patterns as being made up of parts and as also recognising that those parts are a part of a whole (Clements, 1999)

The skill of subitizing contributes to children’s mathematical understanding because...

• It helps children to develop efficient addition and subtraction strategies because they are able to see objects as parts of a whole. E.g. by being able to subitize 5 and 3 makes it easier to develop count-on methods when adding two groups of numbers together – five...six, seven, eight. So there’s eight dots all together
• Being able to subitize also assists children to better understand number families – or the concept of the inverse relationship between subtraction and addition, or even addition and multiplication E.g. Using a five-frame: “I know that there’s three there, and if I add two more, it will be full so I know there will be five. Then if I take three away, there will be two left”.

Resources to develop subitizing skills:

Dice games (perceptual subitizing) – e.g. teddy bear races (Board of Studies NSW, 2002)
Motivates children to recognise the number of dots on the dice quickly



Quick images.... (Clements, 1999)

With dotty plates (to develop perceptual subitizing) E.g. Flash a dotty plate at the children and quickly take it away, then ask "How many dots were on that plate?"

These plates were made according to Clements' (1999, p. 403) guidelines for introducing children to subitizing:

1. Groups should not be embedded in pictorial contexts
2. Simple forms such as homogenous groups or circles or squares rather than pictures of animals or mixtures of any shapes should be used for the units
3. Regular arrangements should be emphasized, and most should include symmetry, with linear arrangements...and rectagular arrangements
4. Have good figure ground contrast

With Ten-frames and five-frames (to develop conceptual subitizing)

How many are there?
Six
How did you work it out?
I saw two groups of three
I saw there were four sqaures left and I know that 10 - 4 = 6

References:
Board of NSW. (2002). Developing efficient numeracy strategies: stage 1. Sydney: Department of Education and Training

Clements, D. H. (1999). Subitizing: what is it? Why teach it? Teaching Children Mathematics, 5(7), 400-405