As mathematics teacher and learning coach Andrew Stadel explains, problems can help mathematicians develop their number sense and problem solving skills. Stadel has created Estimation 180, a compilation of classroom activities and lesson plans that center on the skill of estimation. The name of the site comes from the 180 short estimation problems (one for each day of the school year) that are at the center of this project. Each of these problems include a picture accompanied by an estimation problem (e.g. How many sheets of paper are in this box?). Students or classrooms are invited to fill out a Google Form with their estimate and reasoning and explore other responses (along with the correct answer.) These problems offer a useful series of anticipatory sets for elementary school classrooms. In addition, mathematics teachers may want to check out the Clothesline Activities and the Lessons sections for some more ready-to-use classroom materials.