What is subitizing and why should I teach it?
Subitizing is looking at a group of objects and knowing how many are there, without individually counting each one. It is a key skill for children to learn and practice, as it helps develop number sense, decomposing and composing numbers, strategies of counting on or counting backwards. It is a critical skill that should be practiced in every kindergarten classroom and is very easy to implement.
Tell Me Fast Subitizing Routine
The easiest routine for practicing subitizing is known by many names, like Quick Images, Quick Pictures, or Tell Me Fast, which is what I call it. In this routine I grab a set of cards and move it quickly in front of the students on the rug. Then I cover it and ask them to put a thumb on their knee if they saw how many were there. Next, they share how they knew, and we see if others agree. I repeat a few more times with different cards.
This is a very quick activity that I use as an opener for my math lessons or closers at the end of math. It takes maybe 5 minutes. It’s especially great as a transition activity to or from math as kids are settling down to the rug, they can start participating in the math warm up, or you can dismiss kids to recess or the next activity after they share their answer. You can get through the whole class quickly because it is such a fast-paced activity.
You can also start out Tell Me Fast with just your fingers – show your fingers then hide them behind your back and ask how many fingers did you show!
Other Classroom Subitizing Activities
In the same idea as the Tell Me Fast cards you could make powerpoints with quick images and then a blank slide to ask students how many they saw. Similar to these, are Splat powerpoints where a color splat will cover some of the dots. These were created by Steve Wyborney and are free on his website. These are perfect for later in the year when children are working on decomposing numbers. Jack Hartmann also has a bunch of different subitizing videos that are fun for the kids but keep them practicing their subitizing skills. DreamBox also has a really great free resource for subitizing numbers to ten and twenty on a ten frame or on a rekenrek.
Another activity is to take the Tell Me Fast cards and give it to the students to practice with. Students could put down counters on top of the dots or images to practice one-to-one correspondence (to help realize that each dot/image represents a number) and to help practice seeing groups of numbers in one larger number. As they progress, students can even add equations. Another activity is to have students partner up and act out the Tell Me Fast with each other, taking turns flipping the image and being the guesser. Work with students to ask their partners how they saw the images. If the cards are laminated, they can use a dry erase marker to circle the groups of numbers that they saw.
When starting the year in kindergarten, I suggest starting with subitizing numbers to five. Let the students get very comfortable with seeing numbers to five in a variety of formats and objects. After they are comfortable with numbers to five, start with numbers to ten. I would only do one object/color at first. I would do images and dots on a ten frame. I would talk about seeing smaller groups of numbers inside these numbers, like a group of two dots and a group of four dots makes six dots. I would also connect the groups they see, when applicable, to the dice model of dots, which they are so familiar with.
After they get comfortable with numbers to ten, around November/December, I would start showing images with more than one color or kind of object to start talking about breaking apart the numbers. In January/February I add in using equations to show our thinking about the images we see. At first I write the equations based on what they are saying and then eventually I have them verbally say or write down the equations for how they see the dots.
When I teach teen numbers, which for our curriculum is around December and then again in May (to talk more about breaking apart teen numbers into tens and ones) I start to use Tell Me Fast cards with teen numbers in them, always using the ten frame model to support their understanding that teen numbers are a group of ten and some more.
Around April/May I start changing the focus of my questions to focus on the strategy used for seeing the total number. I want my students to be able to count on or count backwards, depending on what makes the most sense for the image they are seeing. When I start focusing on this, I always use ten frame or rekenrek images (tools they are familiar with and have a set number of numbers on the top row and the bottom row). We talk about the strategies and I also model using the strategies. For example, I might say, “Oh I noticed that there were two squares without dots in them. Instead of counting each dot, it would be faster to count backwards, since I know there are ten squares but only two are missing dots.” Not all the students will get there by the end of kindergarten, but it is good to expose them to these different strategies so they can see which ones help them the most.
Change It Up
Don’t just use images in a ten frame or a straight line! Part of the benefits to practicing subitizing is to see numbers in a variety of formats and settings in order to really have a strong number sense about those numbers. You can also mix and match within a set of cards! Jack Hartmann does a great job of this in his videos – he shows finger images, then dots, and then tally marks. Here are some examples of different ways to show images without always using a ten frame.
Subitizing Teacher Language
The questions you ask during the Tell Me Fast can really extend your students’ thinking. When I ask students to put a thumb on their knee when they know how many, it is because I do want to give students a chance to think about what they have seen without feeling pressured by their peers knowing already. When I call on a student to share what they saw, I always ask first if others agree, and if not what number did they see. (This is a great lesson on it is ok to disagree, mathematicians don’t always get the same answer but then they discuss the different answer and double check their work.) Another option, if the number is between 1-10, is to have children show on their fingers the total number. They should keep it right in front of their chest so that their peers can’t see.
If everyone agrees, I ask the student how they saw that number. I flip over the card again so they can show the groups of numbers they are talking about. Then I always ask other students to share how they saw it by asking, “did anyone see it a different way?” This is a great way to talk about how people can see things different ways, and both are ok! It is also a great way to share each other’s strategies so that maybe next time they will try a different strategy! We go through a few different strategies per card and then move on.
If there is disagreement about how many are on the card, I ask for all the different answers people have. I simply say, “Ok. Any other ideas?” (I do not want to give my opinion). Then I flip over the card and say, let’s all double check, and then we count together. Once we all count, I ask the students who saw that amount, how did you see that number?
Subitizing is an important skill to practice in kindergarten and there are many easy ways to implement them in your classroom routines. Teachers should be purposeful about the images that they choose and the language they use. When subitizing becomes a routine in your classroom, you will see so much growth in your students over the year and you will definitely see that transfer to other math skills they are learning.