Angle measurement — for parents
Year 4 is the first year angles get a careful workout. Children meet the vocabulary (vertex, ray, degree), learn to classify angles, and use a protractor to measure them precisely. It is also the year they connect angles to fractions of a full turn.
What your child should master by year-end
- Identify the parts of an angle: vertex and two rays (or arms).
- Classify angles as acute (< 90°), right (= 90°), obtuse (> 90° and < 180°), or straight (= 180°).
- Use a protractor to measure an angle to the nearest degree, choosing the right scale.
- Know that a full turn is 360°, a half turn is 180°, a quarter turn is 90°.
- Match angles to fractions of a full turn (quarter, half, eighth, twelfth).
Common mistakes
Reading the wrong protractor scale
Most protractors have two scales — one running 0→180 from left to right and one 0→180 from right to left. Children often read the wrong one and get an answer like 130° when they should have read 50°.
Help: before reading, get them to guess whether the angle is acute or obtuse. If they then read 130° for an acute-looking angle, they know to switch scales.Centre point not on the vertex
The protractor centre must sit exactly on the vertex. Even a millimetre off and the reading skews. Tell them to put a fingernail on the vertex and rotate the protractor around the nail before placing it.
"Right angle" vs "right" direction
Some children confuse the word "right angle" with the right-hand side. A right angle is exactly 90° — it has nothing to do with which way the angle opens.
Help: emphasise the picture (square corner) rather than the word. The corner of a book is a right angle no matter how you rotate the book.Adding angle types together
When two angles share a vertex, children sometimes don't realise that the combined angle is the sum of the parts. A 30° angle next to a 50° angle makes an 80° angle.
Help: a folded paper trick. Fold a square corner (90°), then unfold and fold smaller angles inside it. Add the parts to confirm they make the corner.Things to try at home
Clock-hand angles
At each "o'clock", ask: "What's the angle between the hour and minute hands now?" Three o'clock is 90°, six o'clock is 180°, twelve o'clock is 0°. Other times need a little estimation.
Folding paper
Fold a square sheet of paper diagonally. The angle at the fold is a right angle (90°). Fold again to make a 45° angle. Fold once more for 22.5°. Children see angles halve every time.
Open the door
How wide is your door open right now? Stand at the hinge, look at the angle. Use a protractor (or guess) — is it acute, right or obtuse?
Understanding the protractor
A protractor isn't magic. It is a semicircle divided into 180 equal parts, with each line marking 1°. The numbers go in both directions because angles can open either way — clockwise or anti-clockwise. The two scales are just two ways of reading the same physical marks.
Once your child understands that there is one set of tick marks but two numbering systems, the "wrong scale" mistake disappears.