Lesson Standard: 3.MD.8 Solve real-world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and exhibiting rectangles with the same perimeter and different areas or with the same area and different perimeters.

Content Objective: Students will come to understand what perimeter means and will be able to find perimeter by adding all the side lengths around the shape.

Mathematical practice(s): 1 Make sense of problems and persevere, 3 Construct viable arguments, 4 Model with mathematics, 7 Look for and make use of structure

Lesson Design / What will the teacher be doing? / What will the students be doing?
(Structured Student Interaction) / What will the teacher be listening for?
(What do we expect students to say?) / Probing Questions for Differentiation
Assessing Questions
(“stuck”) / Advancing Questions
(further learning)
Engage (Launch)
Predict how many whiteboard markers it will take to go around the desk. / Teacher will hold up a whiteboard marker and ask students to predict how many white board markers it will take to go around the desk.
Teacher will have students share their estimate and how they got their answer with their partner. / Students will estimate how many whiteboard markers it will take to go around the desks.
Students will share their estimate and how they got their answer with their partner. / Adding
Side lengths (number of markers) / Is your answer reasonable?
Activity or Task 1
Draw a rectangle on the board with a grid inside the shape. What would this side measure be? (3 units). What would this side measure be? (4 units) Using those measures, how can you determine the total number of units around the shape? / Teacher will draw a rectangle on the board with a grid inside the shape. What would this side measure be? (3 units). What would this side measure be? (4 units) Using those measures, how can you determine the total number of units around the shape?
Teacher will write the number sentence as students call out the numbers to add.
Everyone tell me what the perimeter is? / Students will use the measurements to find the perimeter of the shape.
Students will call out their answers. / 14 units / Some people said 12. What were they counting?
Some people said 14. What were they counting?
Activity or Task 2
Have students find the area of the “L” shaped figure. (Reteach page R 87 #2) / Teacher will draw an “L” shaped figure on the board with grid lines. Have students find the area of the “L” shaped figure.
Teacher will draw students’ attention to each line segment that makes up one side length. (possibly use a highlighter to outline the figure) Have students count the line segments to find a side length. Then ask students the next side length without modeling counting line segments.
Teacher will write the number sentence as students call out the numbers to add. / Students will find the perimeter of the “L” shaped figure.
Students will count the line segments to find a side length.
Students find the next side length without the teacher modeling counting line segments. / Forget to include certain sides of the figure. / Can you write a number sentence to find the perimeter?
Activity or Task 3
Students will find the perimeter for problem #1 on page 435. / Teacher will give each student a copy of the problem (or students can use the problem in their book.
Teacher will look for a potential START.
Teacher will write the number sentence as students call out the numbers to add. / Students will solve for the perimeter on their own paper.
Students will share their reasoning and answer with their partner.
Selected students will share their reasoning and answer with the class. / Forget to include certain sides of the figure / Why is 12 a smart mistake? / How many different number sentences can you write to find the perimeter?
Activity or Task 3
Students will find the perimeter of the shape on page 436 #8. / Teacher will handout the paper with the shape and have students find the perimeter independently.
Teacher will ask students to give side lengths. Teacher will strategically skip one of the sides that measures 1. Add all the side measures – write the number sentence below. Ask students to agree to disagree with the answer. Have a student that disagrees explain why. Explain the error. Revise the answer as a class. / Students will find the perimeter of the shape independently.
Students give side lengths. Students agree or disagree with the answer.
A student that disagrees explain why. Explain the error.
Revise the answer as a class. / Forget to include certain sides of the figure / Why is 22 a smart mistake? / How many different number sentences can you write to find the perimeter?
Closure
Ticket out the door …. Find the perimeter of a figure with given sides. / Students solve the Ticket out the door independently.

Find the perimeter of this shape.


Find the perimeter of this shape.