Subitizing: Why, When and What Is It?


Subitizing can be one of those skills that we know our students need to have but we aren't sure when or how to go about making this happen. I want to clear subitizing up for you and to give you some "I can implement this tomorrow" activities to use in your classroom.

Let's start with a definition: Subitizing is having the ability to look at a picture or a set of objects and to know how many their are, almost instantly, without counting. Playing a dice game would be a most basic example of subitizing. When you roll a die, you look down and know immediately that you rolled, for example, a 3. You didn't need to count the pips to know, without a doubt, how many dots their are. Subitizing is a foundation upon which number sense is developed. 

Subitizing, however, goes beyond this initial ability. The type of subitizing I am referring to is called perceptual subitizing. You are perceiving "how many" almost instantly through sight. A second type of subitizing is called conceptual subitizing. Conceptual subitizing is better explained through the example of rolling two dice. You roll a pair of 5s and know, almost immediately, that you have rolled a 10. You didn't count each of the pips on the dice but you know the pattern of 5 and 5 making ten and therefore can quickly and accurately report "how many".

So, how can you make these two types of subitizing work for you and your students? In terms of perceptual subitizing, expose students to a number of "regular" representations of amounts. I have listed 6 suggestions off to the side but they are really just the tip of the iceberg.

Students can work with these representations in a variety of ways and that is really the focus, students experiencing the representations over and over and over. You can try card flashes with ten frames or fingers having students answer as rapidly as they can. You could ask students to match a numeral to the ten frame it represents in a game of memory. Students can play a game of dominoes stating aloud the numbers they are matching together, students can play board games that require them to roll dice, you can practice counting aloud to ten with students holding up their fingers as they go, you can have students play memory with a deck of cards either with or without the face cards.

Obviously there are SO many options!! As for when to use these activities and how often you should be working on subitizing with students I would say that you could do the full group activities as a math warm up, when your students are in line waiting to go somewhere or really any time you have 1-3 minutes to fill. Many of the other activities make a quick and easy math center that students can work on until these regular patterns start to become second nature to them.

Once students are solid subitizing regular patterns to 5, I am sure to incorporate activities that focus on conceptual subitizing. The type of activity requiring conceptual subitizing that I focus on depends on the math skill I am developing.

We know from the work of John Van de Walle in his book "Teaching Student Centered Mathematics"  that number sense is built on a foundation of spatial recognition, the relationship of one more and one less, part part whole relationships and benchmarks of 5 and ten. Conceptual subitizing activities are obviously related to spatial recognition but can boost each of the other 3 understandings as well. In terms of a few examples, students can solidify their understanding of one more and one less  through practicing thinking about patterns they know and what that number would be if you added one or took one away. Fact fluency for the 5+ facts can be grounded in a foundation of spatial understanding of dot patterns as well.

Comment down below with either an activity you could do to boost your students subitizing skills using one of the representations listed- let's get a bank of quick activities going!

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