Bridges in Mathematics

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Mastering the Skills of Estimation

Marion Leonard

Children need lots of practice, with various activities in different settings, to develop a strong sense of number. My kindergartners love an activity I call Estimation Bag. I place a small plastic container inside a canvas bag, and a student adds a single type of object: paperclips, pennies, barrettes, etc. We start with 10 or fewer and increase the quantity to between 10 and 20 after a month or so.

Here is the routine to start your own Estimation Bag. I use a canvas bag decorated with ????, numbers, and the label Estimation Bag. Directions for a parent to read are on an index card attached to one of the bag’s handles. A clear quart-size container works well to hold the objects. With classmates seated around the rug, the selected student walks around the circle to give them a quick glance.  

Mastering the Skills of Estimation

When everyone has seen the container, students write their guess on their dry-erase board. We go around the circle and quickly state our guesses.

Mastering the Skills of Estimation  

The student announces whether anyone has the correct answer … always a big deal! Then comes the fun part!

As suspense builds, the student slowly fills ten-frames to reveal the quantity. We stop filling at a critical point. 

Mastering the Skills of Estimation

If the number is larger than 15, we initially fill to 15; if it is larger than 5 but smaller than 10, we stop at 5. We have conversations about the current guesses and whether they could be accurate or not. The remaining objects are carefully and secretly hidden under a mat and arranged in a pattern for a quick reveal! I lift the cover, reveal the final amount, and then quickly cover it again.

Mastering the Skills of Estimation

Students are allowed to correct their initial guess, so everyone feels successful. Of course, we celebrate those who guessed correctly or were very close with a “neighbor” number.  

This activity really helps my students become accustomed to estimating and recording their guesses while working with a variety of quantities!