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Estimation – What Strategies Do You Teach? How?

Research indicates that the vast majority of all calculations performed by adults in everyday life involve mental math…and that estimates are sufficient for around 60% of all our daily calculations.2  Yet further research repeatedly reveals that a majority of both K-12 students and college-educated adults have difficulty using estimation.1

This leads us to several interesting questions:

1)      How do we use estimation and mental math each day?
Consider yesterday – when, how, and how often did you use estimation?

2)      How do we think the adults/older youth we teach use estimation each day?

3)      What are some solid strategies for strengthening our learners’ estimation skills?

Please share with us your thoughts on estimation – its importance both in and outside the classroom, how you address it, any ‘ah-has’ you’ve had, etc.  Below are some comments from our Math Content expert, Donna Curry, to get you started:  Are you familiar with the estimation strategies she mentions? Do you teach them to your learners? How?

“Many folks are not aware that there are different strategies for estimation depending on your purpose or the situation. These different strategies, as well as how/when to use them, should be explicitly addressed with our adult learners.

Rounding is one strategy commonly presented in textbooks, but you can also do front end estimating (just looking at the digits furthest to the left – such as looking at 23 + 45 + 31 and changing them to 20 + 40 + 30 for an estimate).  Or, you could clump numbers to get similar clumps (such as 1.24 + 2.38 + 4.70 + 8.64 and clump 1.24 & 4.70 together to make about 6 since .24  + .70 is about 1, and then clump 2.38 & 8.64 to make about 11 since .38 and .64 is about 1).  In fact, even with rounding there is no “law” that requires that you round up or down – for example, when shopping I always round up to make sure I have enough money. When estimating, you always need to decide what makes sense for the situation (or your purpose)!

We need to help our learners realize that an estimate is used to get a sense for the number. In this way estimation is key to number sense. (It is not simply another chapter in the book!)” – Donna Curry

We look forward to your thoughts on Estimation and Estimation Strategies!

Learn more about teaching estimation strategies in the EFF online mini-course, How Close is Close Enough?: Improving Estimation Skills, or via other EFF professional development materials/services!

 Research on the Use of Estimation:

1Adding It Up: Helping Children Learn Mathematics, (2001) Jeremy Kilpatrick, Jane Swafford, Bradford Findell, National Academy Press Washington, DC.

2 Northcote, M., & McIntosh, M. (1999) What mathematics do adults really do in everyday life? Australian Primary Mathematics Classroom, 4(1), (pp19-21)