Estimation 180: Improving Number Sense

In October of 2012, Andrew Stadel, a middle school math teacher, created a website called Estimation 180, with the goal of helping his students improve their number sense. Andrew considers estimating key to developing number sense and reason (we are inclined to agree). He teaches Pre-algebra, Algebra and Geometry, so his estimation challenges are not limited to a specific grade level.

Every day, Andrew gives his students an estimation challenge around a theme.  He reveals a picture of an object, and students make an estimate about the object’s height, weight, or other measurement.  Each chooses a number that is too high, one that is too low, and finally their estimate, allowing ALL students entry into the challenge. In addition, he asks his students for their reasoning, a great way to explicitly teach – and for students to engage in – Math Practice #3: Construct viable arguments and critique the reasoning of others.   There is potential for some great math talk here.

Estimation Challenge - Day 1

Estimation Challenge – Day 1

He’s also created a worksheet for students to keep track of their estimates, their reasoning, and their error percentage.  It is a great way for students to track their own progress (a research-based strategy with a high effect size).

As an engaging extension, students and classes can submit their estimates right on the webpage, compare them to participants outside of their classroom, and see the reasoning behind others’ estimates.

Estimation Challenge – Day 53

Andrew has recently added a tab with lessons ranging from 4th – 8th grade that are focused on a particular Common Core Standard. His infamous File Cabinet task (picture below) is among those lessons he is sharing.   A fan of 3-act tasks, Andrew cleaned up many of those found in his original 3-act catalogue, tagged them with Common Core Standards, and now includes handouts to go with the lessons.

File Cabinet Task

Act 1 of the File Cabinet Task

When we think of someone who walks the walk with regard to what it means to teach with the math practices in mind, Andrew Stadel is one who comes to mind. He incorporates student collaboration and problem-solving into his lessons while balancing the need for individual think-time and accountability.

You’ll find Estimation 180, as well as a link to Andrew’s blog, Divisible by 3 on our Math Symbaloo. The math half of us would LOVE to model this in your classroom.

 We encourage your comments.


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