Montessori At Home: Estimation Jar

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Estimation is a mathematics skill that we all use every day. We might estimate how many people are in a room, how much our dinner bill might cost, or how long it might take to get through a queue! Estimation skills begin with basic numeracy and practice, and an at home estimation jar is an engaging and instructive tool, plus it can be fun for the whole family! 

An estimation jar is a clear jar with a certain number of one item inside (for instance, 5 golf balls or 100 beans). Everyone in the family should take turns guessing or estimating how many items there are. Each person can write down their estimations and at the end of the week (to build anticipation!) the items inside are counted to see who was closest. 

To make your own estimation jar begin with a medium size clear jar with a lid and place it on a shelf or table where children can reach it. They will need to be able to pick it up, hold it, and look at it from all angles. 

For children around 2 years old use just a few large objects. You can try 3 or 4 balls or blocks. Try to make each object the same size, but a different color. When a child is first learning about counting, and thus is very new to estimation, we want to make success achievable. 

As children age and learn more about numeracy and estimation, you can make the jar more difficult. You can make the objects progressively smaller, and thus the number progressively larger. You can also introduce a “referent”, or a jar with a few of the same object where you tell your child how many there are (for example, “this jar has 20 marbles, how many do you think are in the full jar?”). 

Remember to go slow and keep things at their level, if they don’t know the number 100 there shouldn’t be 100 objects inside. Estimation is tricky and a skill that is learned through a lot of practice! You might even stump yourself! And if you’re stumped on ideas for what to include in the jar, check out this list.  

Video Resource:

My Works Montessori have a wonderful video on this exercise. 

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