A three-page Year 3 sheet on finding perimeter by counting unit edges on a centimetre grid. Page 1 shows eight coloured shapes, A to H: a 3 by 2 rectangle, a 4 by 1 strip, a 5 by 3 rectangle, a 3 by 3 square and four L shapes made of three, four, five and six squares. Pupils write each perimeter in centimetres. On page 2 they draw their own shapes with a perimeter of 12 cm. Page 3 is the answer key. It follows England National Curriculum measurement for Year 3.
Measurement
“measure the perimeter of simple 2-D shapes”
Questions 1 to 8 ask pupils to count the edges round rectangles, a square and four L shapes. Questions 9 and 10 ask them to draw shapes with a perimeter of 12 cm.
Measurement
“measure, compare, add and subtract: lengths (m/cm/mm)”
Every perimeter is in centimetres, and the key shows each count as an addition, such as 4 + 3 + 1 + 3 + 2 + 1 = 14 cm for Shape H.
Pupils count the unit edges around eight shapes on a 1 cm grid and write each answer on a numbered line. Shapes A to D are rectangles and a square. Shapes E to H are L shapes.
A blank 1 cm grid for question 9, a rectangle (Shape R) with a perimeter of 12 cm, and question 10, a different shape (Shape S) with the same perimeter. Pupils draw with a ruler and a coloured pencil.
Each count is written as a sum, such as 3 + 2 + 3 + 2 = 10 cm. The key lists three rectangles that work for Shape R and accepts any shape drawn along the grid lines with 12 unit edges for Shape S.
Before pupils start
Walk a finger round Shape H on the board and count the edges aloud. The L shapes are where pupils most often skip an edge.
Early finishers
Pupils who finish question 10 can draw a second shape with a perimeter of 12 cm and swap with a partner, who checks it by counting.
Exit task
Use questions 9 and 10 at the end of the lesson. A pupil who draws a 3 by 3 square and a 5 by 1 strip has seen that different shapes can share one perimeter.
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