I have been back at teaching middle school for a month now. It has been challenging, amazing, and also so deeply tiring! Years ago I read that the biggest barrier to high school and middle school is lack of mastery of number sense from elementary school. I've tried lots of things as daily routines to help students close this gap but my favorite by far is an idea I got from 4th cohort Desmos Fellow friend Sarah Furman. Sarah shared that she uses Andrew Stadel's Estimation 180 problems but gives her students a clue that allows them to review a key number sense skill. I decided to try it in my classroom and I don't really have words for how amazing it has been. Here is what I do: I give them an Estimation 180 problem that is either from Andrew Stadel's amazing website ( http://www.estimation180.com/ ) or one that I created about myself, my family, or my community: I ask students to write their first guess down. I walk around to get a sense of what they are w...