Classifying Angles: Acute, Right, Obtuse and Straight

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1 Getting Started
2 Watch and Notice
3 Try It Together
4 Draw One of Each in Your Copy
5 Class Challenge
6 What Did We Notice?
7 What's Next
Pupil practice

1 - Getting Started ~4 mins

Illustration for Getting Started Look at the two clocks on the board. On the first clock, the minute hand points to the 12 and the hour hand points to the 3, making a neat square corner. On the second clock, the hour hand moves down to the 6, so the two hands make one flat, straight line.

Key point

That second one is completely flat. What kind of turn made the hour hand go all the way down to make a straight line?

Teacher Notes

Show the two clock positions side by side on the board as pupils settle. Take three hands-up answers, not open call-outs.

You are listening for the idea of a half turn. If a pupil says "it went halfway round", hold that thought, that is exactly the straight angle we meet later.

👇 Mark your steps as done as you complete them.

+5 XP

2 - Watch and Notice ~8 mins

Four angles on the board, each drawn on a protractor so you can see how far it opens. Compare each one to a right angle, the square corner.

Watch which is smaller than the square corner, which fits it exactly, which is bigger, and which opens all the way to a flat line.

Look carefully at the last one. A straight angle is not a wide corner, it is a flat line, a half turn. How many right angles would fit inside it?

Teacher Notes

Point to each group in turn and hold your paper right-angle checker against the shape you name, so the class watches the compare-to-the-square-corner test happen live.

Acute — the square corner is too big to fit inside; the angle is smaller.
Right — the square corner fits exactly.
Obtuse — the square corner slots in with room to spare; the angle is bigger.
Straight — the two arms lie flat in one line. Ask the on-board question "how many right angles could fit here?" and wait for two, with two hands-up answers.

Do not confirm the two-right-angles idea fully yet, let the class carry it to the wrap step at the end.

👇 Mark your steps as done as you complete them.

+10 XP

3 - Try It Together ~8 mins

Now we make each kind of angle ourselves on the board. A pupil drags the ray to open the angle, and the class decides which group it belongs to before we read what the protractor says.

Key point The test is always the same: hold the paper right-angle checker against the angle. Is the square corner too big to fit inside it, does it fit exactly, does it slot in with room to spare while the arms still bend, or do the arms lie flat in one straight line?

Open the angle to each group in turn

Teacher Notes

Talk this one through together — no marking yet. Pupils take turns at the board and the class agrees or corrects out loud before each card lands.

Hand each pupil a moment to hold the paper right-angle checker against the card before they drag it. The whole test is: does the square corner fit exactly, is it too big to fit, or does it slot in with room to spare?

The straight angle is the one that catches people, some will want to call the flat line "obtuse". Head this off: an obtuse angle still has a bend in it; a straight angle has no bend at all.

+15 XP

4 - Draw One of Each in Your Copy ~3 mins

COPYBOOK MOMENT

In your maths copy, draw one angle of each kind and label each one: an acute angle, a right angle, an obtuse angle and a straight angle.

Use the corner of your copybook as your square-corner guide, and put a small square mark inside the right angle to show it is exactly square.

Teacher Notes

Walk the room glancing at the four labels and the square mark on the right angle. This is whole-class copybook practice, not marking.

Watch for the straight angle being drawn with a bend, remind that pupil it should be one flat line.

+10 XP

5 - Class Challenge ~10 mins

Now we make each kind of angle ourselves and sort it. Open the angle on the board, check it against the corner of your copybook, then drag the matching card into its group.

First open it a little to make an acute angle. Then open it to an exact right angle. Next open it wider for an obtuse angle. Last, open it all the way so it makes a straight angle, one flat line.

Match the angle you made to its name

Teacher Notes

This is the practice round. Pupils take turns at the board, check each answer, and the class confirms before moving on. Keep it brisk rather than over-explaining.

A pupil opens the angle on the board, holds the corner of a copybook against it as the square-corner checker, then drags the matching card to its group. Every child has a copybook corner, so nothing has to be made or handed out.

The last move, opening it all the way, is the one to linger on: a straight angle is not a very wide corner, it is one flat line, and two right angles fit inside it. Ask how many square corners fit before you name it.

+15 XP

Pupil practice

Module 7 · 2D and 3D Shapes and Angles Shape & Space

Lesson 87 · Classifying Angles: Acute, Right, Obtuse and Straight

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Teacher Class Feed

1 - Getting Started ~4 mins

2 - Watch and Notice ~8 mins

3 - Try It Together ~8 mins

Open the angle to each group in turn

4 - Draw One of Each in Your Copy ~3 mins

5 - Class Challenge ~10 mins

Match the angle you made to its name

Unlock the full learning experience

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