Hands up: is a square also a rectangle? And is a rectangle also a square? Take a moment to decide what you think, then be ready to defend your answer to the class.

Look at the sides and angles marked on some triangles, then two four-sided shapes and a trapezium. Notice the marks and see what makes each shape different from the others.

The shapes from today are on the board together. We will name a property, such as 'has two pairs of parallel sides' or 'has a right angle', and then inspect each shape in turn to see whether its marks show that property. We agree as a class which ones fit before we move on.

Today we sort shapes into groups by their properties. First we sort triangles by their angle type: right-angled, acute or obtuse. Then we sort quadrilaterals into an overlap: shapes with parallel sides, shapes with all sides equal, and the shapes that belong in both.

What we did today

• We sorted triangles by their sides and by their angles, and quadrilaterals by their parallel sides and equal sides.
• We learned that every square is a rectangle, because a square has every rectangle property plus four equal sides; but not every rectangle is a square, because four equal sides is not required of a rectangle.

Coming up

Next we use a ruler and compass to construct triangles from given measurements, so that only one triangle can be built from the right facts.