Checking understanding of similarity
I can enlarge a shape and can state what changes and what is invariant.
Checking understanding of similarity
I can enlarge a shape and can state what changes and what is invariant.
These resources will be removed by end of Summer Term 2025.
Lesson details
Key learning points
- An enlargement means a change in size.
- The lengths of the lines may change when enlarged.
- The angles inside an object do not change when enlarged.
- When an object is enlarged, the image is similar.
Keywords
Object - The object is the starting figure before a transformation has been applied.
Image - The image is the resulting figure after a transformation has been applied.
Similar - Two shapes are similar if the only difference between them is their size. Their side lengths are in the same proportions.
Scale factor - Scale factor is the multiplier between similar shapes that describes how large one shape is compared to the other.
Invariant - A property of a shape is invariant if that property has not changed after the shape is transformed.
Common misconception
When a pair of similar shapes are not in the same orientation, pupils may select an incorrect pair of lengths to calculate the scale factor.
Encourage pupils to take a systematic approach to locating pairs of corresponding lengths by looking for the longest edge in each shape, then the second longest, third longest, etc.
To help you plan your year 9 maths lesson on: Checking understanding of similarity, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 9 maths lesson on: Checking understanding of similarity, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 3 maths lessons from the Geometrical properties: similarity and Pythagoras' theorem unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
Licence
Starter quiz
6 Questions


$$a\text{ }$$ cm -
8 cm
$$b\text{ }$$ cm -
6 cm
$$c\text{ }$$ cm -
10 cm
Exit quiz
6 Questions


