- Third Grade
- 85 minutes
- Standards: 3.MD.D.8
In this lesson, students will find the perimeter of figures using cheese crackers. Next, they'll design a floor plan for their cheese cracker dream house, to help them practice and retain the formula for finding perimeter.
Students will be able to find the perimeter of a given geometric figure.
Introduction (10 minutes)
- Play the video Perimeter, by Math Antics, for the class to introduce the concept of perimeter.
- Once the video is complete, ask for a volunteer to tell you the definition of perimeter.
- Write the definition on the board.
- Draw a few figures on the board, along with the lengths of their sides.
- Challenge students to find the perimeter of the geometrical figures you’ve drawn.
- Each time a student answers, correctly or incorrectly, explain the reasoning behind each figure’s perimeter.
Explicit Instruction/Teacher Modeling (20 minutes)
- Start by showing your students how to use unit squares to count the perimeter units of a figure. For example, find an object in the classroom, such as a book, to measure.
- Using the cheese crackers (or the unit of your choice), model how students would find the perimeter of the book by placing crackers side-by-side, all around the book.
- Write the unit measurements on the board, and then ask the class to find the perimeter.
- For example, if the object you measured is 3 crackers on one side, by 7 crackers on another side, the perimeter (total) would be 3 + 3 + 7 + 7, or 20 crackers.
Guided Practice/Interactive Modeling (20 minutes)
- Once you’ve finished modeling finding the perimeter, tell students to make a 3x5 array (rectangle) with the cheese crackers.
- As the class creates the rectangle, ask students to find the perimeter when they’re done, and record the perimeter in their math journals.
- Once the class is done, demonstrate how to draw a 3x5 rectangle, and how to find the perimeter, using a projector or document camera.
- Have students create a 2x10 rectangle this time, and repeat the process. Walk around the class to support students, as they need it.
- Pass out copies of the Find the Perimeter worksheet (see attached).
- Model two of the problems for the class on the board, with a document camera or with a projector.
Independent Working Time (20 minutes)
- Have students finish the rest of the Find the Perimeter worksheet independently. If students get stuck, have them raise their hand for your assistance.
- As students complete the worksheet, check their answers.
- Students who successfully complete the worksheet should move on to their application project, creating a Dream House.
- Tell the class that each person will create a floor plan for their dream house, using cheese crackers to design and measure their layout.
- Once they’ve created a floor plan, have students record it in their math journal. The math journal should include a drawing of the floor plan, and the perimeter.
- Enrichment: Students who need more of a challenge can build multiple floor plans (for a multi-level dream house) during independent working time. You can also have these students find the area in addition to the perimeter.
- Support: Arrange students who are struggling into a small group to work with you. Complete the Find the Perimeter worksheet as a group, using cheese crackers as manipulatives.
Related Books and/or Media
- Spaghetti and Meatballs for All! by Marilyn Burns
- Perimeter, Area, and Volume by David Adler
- Video: Perimeter Song by Adam Up Maths
Assessment (5 minutes)
- Review your students’ worksheets and dream house floor plans to assess their understanding of perimeter.
Review and Closing (10 minutes)
- Students will complete “Perimeter Four Square Review” as their journal reflection.