Why Delay Formulas?

Have your students gotten mixed up with area and perimeter formulas? When a formula is introduced too soon, some students apply the formula without understanding the meaning. If you delay formulas and focus on the meanings, students are more likely to succeed with area and perimeter. Ask students to think about various ways to find the perimeter (distance around) or area (square units inside) a shape.

Area Perimeter Rectangles

Discuss rectangles such as the ones shown above. Here are sample questions and answers.
  • How can you find the distance around the 3-by-8 rectangle? [Sample answers: 3 + 3 + 8 + 8 = 22, or 3 + 8 = 11 and double it to get 22, count all the way around]
  • How can you find the area of the 5-by-6 rectangle? [Sample answers: 6 rows of 5 is 30, count by 6s]
  • Can two rectangles have the same perimeter but different area? [yes, both rectangles above have perimeter 22 units]
  • Can two rectangles have the same area but different perimeter? [yes, a 10-by-3 rectangle has the same area as the 5-by-6 rectangle but the perimeter is 26 rather than 22]
To promote discussion about area and perimeter, download a FREE card set from TeachersPayTeachers. This set comes with 36 cards to match, a recording sheet, and instructions for four games. More area and perimeter card sets are in the Grade 3 bundle at  TeachersPayTeachers.