# Mathematical Practice 8

## Teacher Behavior

• Engage students in discussion related to repeated reasoning that may occur in a problem's solution
• Draw attention to he prerequisite steps necessary to consider when solving a problem
• Urge students to continually evaluate the reasonableness of their results

## Student Behavior

• Notice repeated calculations and look for general methods and shortcuts
• Continually evaluate the reasonableness of immediate results (comparing estimates)
• Make generalizations based on findings

## Fourth Grade Example Video

In 4th grade, students work on a number talk asking them to evaluate the reasonableness of a two-digit problem and solution--to see if the problem is true or false without solving. As students discuss e rationales for determining why 62+ 78 is or is not equal to 238. Various students offer responses that the numbers are "too small" or "would have to be bigger." Students eventually conclude that adding two two-digit numbers cannot, no matter what, equal more than 198.