“So then after I multiplied the two numbers, I rounded the answer to the nearest hundred to get the estimate.”

This is a common explanation I’ve heard over the years from students as they wrestle with the purpose of estimation.  One of my follow-up questions has usually been something like, “If you already know the exact amount, why would you need to estimate?”  Usually these students are just trying to get the “right” answer, or they are students who are still afraid to make a mistake so they calculate the exact answer and then work backwards to get the answer they think I’m looking for.

Hopefully this year I can use Estimation 180 to give my students a wider variety of real world estimation opportunities!  Each question on the website is accompanied by a picture (you could easily bring in many of these actual objects to your classroom for students to see and touch) and prompts to think about what estimate would be too high and too low before students settle on their answer.  I also like how many of the challenges build on what they discovered the day before.  It lets students consider prior knowledge and comparison as they try to make an accurate approximation.  The other feature that is convenient and exciting is that there are situations that deal with length, time, weight, volume, money, Legos, bacon, and much more!  Really, this site had me at Legos and bacon.

I’m not sure Estimation 180 will address the aspect of estimating that involves rounding numbers to make the calculations easier to do mentally.  Perhaps as my students and I engage in these questions they will at least become more comfortable with being wrong about an estimate, and working off of past mistakes to try to be more accurate in the future.

When I reflect on when I actually approximate values in my day-to-day, it normally occurs in conversation with someone else.  The exact amount is not necessary, but I’m just trying to communicate about how much time something will take, or about how much something will cost, or about how big or small something is.  I probably need to regularly present my students with scenarios where no paper or pencil is involved, because I feel like that has more relevance to why and when we estimate.  We estimate when we have neither the ability or necessity or time to calculate the exact value in our current situation.