Subitizing, being able to quickly recognize the total amount without having to count each member of the group, is an important part of developing number sense. In the primary grades, students who subitize are able to count on from the subitized number. In upper elementary, students can use subitizing to break a larger group into smaller equal groups to find the total.

In this 10 x 10 grid, I used colored sticky dots to create opportunities for students to subitize. Students can find the total number of dots in one of the “triangles” by quickly adding the subitized sets of dots. For example, a student could add the 4 and 2 yellow dots to get 6 then add the 1 and 3 blue dots to get 4 then add 6 + 4 to arrive at 10 total dots.

Young students can simply count the dots by ones. They may choose to count all of them or just the yellow or blue dots.

Older students can find the total number of dots by multiplying 10 dots x 4 (subitized) triangles = 40 dots. If they want to determine how may blank squares there are in the grid they can determine the total number of squares in the grid by multiplying 10 x 10 then subtract 40 from the 100 squares to get 60 blank squares.

There are also a variety of patterns students can notice.  For example, young students can quickly notice a color pattern of blue and yellow.  Older students may notice and even/odd pattern – blue dots are odd numbers and the yellow dots are even numbers.  Some students may even look beyond the dots to the squares in the grid.  An even number pattern emerges here.  Starting at the bottom of the grid, the blank squares skip count by twos:  2, 4, 6, 8, 10 and then back down 10, 8, 6, 4, 2.

Here’s what it looked like at the event:

Here’s a sampling of student thinking: