The students bring rich math strategies with them to grade three. Most of the strategies we generate come from the student’s ways of thinking about numbers. This is good because it often helps them see that they already have good ways of working with numbers. Some of our best thinkers don’t believe they are good at math. Helping kids use and refine their own strategies is the best way we can help them become more confident and value their own thinking.

Estimating Sums: We use the following three strategies to help us build mental math skills. We focus on learning the strategies and practice deciding which strategies gives the best estimate based on the numbers presented in the problem. I can understand that some people may have a glance at the examples below and feel that it seems a bit silly to estimate. I can reassure you that it is worth the short time we spend on it. Many of the mental math strategies people use resemble some of these estimation strategies. For students who are having a tougher time breaking apart numbers and reconstruct them in their mind, estimation is a good first step. It helps them find an easy way to “get close” to the sum or difference and learn to clean up the left over bits later. Students who already have favorite mental math strategies often discover new ones as we discuss estimation. Once they have a few strategies to work with, they can begin learning to choose the most efficient strategies to use depending on the numbers presented in the problem. In short, we have very rich conversations and great thinking springs from our simple estimation strategies.

1. Take both numbers to the closest 10.

59+23
60+20=80
So, 59+23 is estimated to be 80.

2. Take one number to the closest 10.

59+23
60+23=83
So, 59+23 is estimated to be 83

3. Add only the digits in the tens place.

59+23
50+20=70
So, 59+23 is estimated to be 70.