Perimeter Mastery Challenge
Year 4 Mathematics 30-minute lesson Calculating perimeters of 2D shapes
Learning Objectives
Calculate perimeter of rectangles, squares, and composite shapes Use centimetres and metres correctly Apply strategies like addition and doubling Solve real-life perimeter problems Explain mathematical reasoning clearly
What is Perimeter?
The distance around the outside of a shape Measured in units like cm or m Add up all the side lengths Like walking around the edge of a playground
Starter Activity: Quick Recall
Draw a rectangle on your whiteboard Label the sides: 4cm and 6cm Calculate the perimeter Remember: add ALL four sides! 4 + 6 + 4 + 6 = 20cm
Perimeter Formulas
Rectangle: length + width + length + width OR: 2 × length + 2 × width Square: 4 × side length Composite shapes: add all outer sides
Units Matter!
{"left":"Centimetres (cm)\nMetres (m)\nUsed for smaller objects like books, desks","right":"Used for larger objects like rooms, gardens\n100 cm = 1 m\nAlways include units in your answer!"}
Worksheet Practice
Work in pairs on your worksheets Calculate perimeters of simple shapes Check each other's work Remember to include units! Raise your hand if you need help
Real-Life Challenge
A rectangular garden is 8m long and 5m wide How much fencing is needed to go around it? Discuss your method with your partner Be ready to explain your thinking!
Composite Shapes Challenge
Shapes made from rectangles joined together Find the perimeter of the whole shape Only count the OUTSIDE edges Don't count edges inside the shape
Extension Activity
Design your own garden or playground Use squares and rectangles Label all measurements Calculate the total perimeter Challenge: use both cm and m units
Quick Quiz
What is the perimeter of a square with sides of 7cm? A rectangle is 10m long and 3m wide. What's its perimeter? Why do we need to include units in our answers?
Key Points to Remember
Perimeter = distance around the outside Add ALL the outer sides Include units (cm or m) in your answer For rectangles: 2 × length + 2 × width For squares: 4 × side length Check your work by counting sides again