The need for estimation and the estimation wall

For the last few months, I’ve really been buying into the power of estimation. It has changed how I teach in a dramatic way. Let me set the stage.

In December, I gave my students this problem on a checkpoint:


I wish I would have taken photos of some of their work. A few gave answers like $340. Others were in the ballpark of $34,000. To say I was disappointed is an understatement.

But to make a long story short, too many of my students made absolutely no sense of the problem. Sure, they knew that a given formula needed was to be used, but in terms of logical answers goes, they were lost. Key skills like using context clues and relevant information, compare/contrasting, drawing from prior experience, and – most notably – number sense, were completely absent in their responses.

Upon handing back their papers the next day, I did everything but rip the SmartBoard of the wall. They felt my disappointment in their responses. I made sure they did. The most disappointing part was the fact that I’ve seen this sort illogic amongst my students for years and have never strategically addressed it…until now. One student even boldly asked, how do you expect us to think logically if we don’t practice doing it? She was SO RIGHT. I was expecting them to do something I hadn’t outwardly emphasized or taught. More on this situation here.

Around the same time, I attended a workshop led by Dan Meyer and remember him asking for estimates for the answer to a problem. It wasn’t his goal for us to better understand the usefulness of estimation, but somehow that was a big takeaway for me. I think it had much to do with the context Dan created and how worthwhile the too low, too high, and just right estimates were to help us make sense of the problem.

Ever since, I’ve been opening class with an estimation challenge at least three times a week . Estimation 180 has been my go-to. The kids love it. Besides addressing the issues I described above, I’ve been intrigued by how the estimation process itself leads to a variety of other conversations related to the context.

For example, this estimation on the capacity of the soda can prompted a meaningful discussion around why the soda can contains more than the stated 12 fl oz that’s printed on the outside of the can.

What’s the capacity of the can (oz or ml)?

Could it be manufacturing error? Or maybe the carbonation bubbles are causing the measured volume to be greater than expected? Or better yet, maybe Coke is out to get us all by covertly filling our cans with even more sugar or, in this case, artificial sweeteners? (Conspiracy theory anyone?) These sorts of tangents abound whenever I post an estimation challenge.

Anyhow, take all of my in-class success with estimation coupled with my knowledge of Jonathon Claydon’s estimation wall and I decided create a space in the hallway outside of my classroom to encourage the entire school to dive in. Hence, the estimation wall (first edition):


The wall consists of several estimation challenges and their associated question, each taped to piece of construction paper. Underneath the construction paper is the answer.

Soon after I completed the wall, here’s what could be seen. Woohoo!


The creation of the estimation wall also served a different, much bigger purpose. It is much bigger than myself and it revolves around school culture. I realized pretty quickly this year that beyond high-stakes exams and AP courses, my school has no real mathematical identity. There are no mathematical initiatives, no clubs, no field trips, no electives. Though it has mathematics in its title and its one of its founding principles, mathematics is not publicly championed at my school for its creativity, wonder, beauty, and usefulness.

I’m on a mission to change that. The sort of cultural shift I’m envisioning at my school will take time, but we’re a small school…so I’m determined to make a difference.