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Students learn how to find the perimeter and area of various 2D shapes including triangles, quadrilaterals, compound shapes and circles. Throughout the topic links are made to algebraic reasoning and estimation. This topic takes place in Term 4 of Year 9 and links to arc length and area of sectors later on.

**Prerequisite Knowledge**

- choose and use appropriate standard units to estimate and measure length/height in any direction (m/cm); mass (kg/g); temperature (°C); capacity (litres/ml) to the nearest appropriate
- unit, using rulers, scales, thermometers and measuring vessels
- compare and order lengths, mass, volume/capacity and record the results using >, < and =
- measure, compare, add and subtract: lengths (m/cm/mm); mass (kg/g); volume/capacity (l/ml)

**Success Criteria**

know and apply formulae to calculate:

- rectangles
- rectilinear composite shapes
- area of triangles
- parallelograms
- trapezia

calculate the perimeters of 2D shapes, including composite shapes;

**Key Concepts**

- Perimeter is a measure of length around the outside of a shape whereas area is the space on a surface.
- Students should be given the opportunity to derive formulae to calculate the area and perimeter of shapes.
- Area is measured in square units.
- Demonstrate a triangle as being half a rectangle so students know to use the perpendicular height in their calculation.
- Demonstrate a parallelogram as having an equal area to a rectangle.
- To calculate the area of composite rectilinear shapes have students break them up in different ways.

**Common Misconceptions**

- Students often confuse area and perimeter.
- Students can forget to include correct units when stating an area or perimeter.
- When calculating the area of a triangle or parallelogram students tend to use the slanted height rather than the correct perpendicular height.

May 1, 2019

In this blog I will share some practical tips for using mini-whiteboards in a mathematics lesson. I use mini-whiteboards nearly every lesson because they help the students show me the progress they are making. When I understand what the misconceptions are I am able to address them in subsequent examples as part of my feedback. […]

April 17, 2019

Demonstrating student progression during a mathematics lesson is about understanding the learning objective and breaking that down into explicit success criteria. Using Success Criteria Take, for example, a lesson on calculating the area of compound rectilinear shapes. The intended learning objective was written on the main whiteboard. Success criteria were used to break down the individual […]

March 26, 2019

Plotting and interpreting conversion graphs requires linking together several mathematical techniques. Recent U.K. examiner reports indicate there are several common misconceptions when plotting and interpreting conversion graphs. These include: drawing non-linear scales on the x or y axis, using the incorrect units when converting between imperial and metric measurements, taking inaccurate readings from either axis not […]