Show it physically: put your pencil mark in one spot on the board baseline, then in another, so the class sees that the mark's position controls the angle. Take two or three hands-up guesses, not open call-outs, and don't confirm yet. Where would the mark go? is the whole lesson in one question.

• 60° — model the five moves slowly; hold out for the count from zero, not 180.
• 110° — ask which scale the mark reads from before you reveal; the obtuse case is where pupils grab the wrong number.
• 25° — the one to linger on. A miscount here shows up as an angle that looks nearly flat. Ask is 25° bigger or smaller than a right angle? as a sense-check.

This round is for talking it through together, so no marking yet — pupils build each angle on paper with their protractors while the board tool is the measure-back check, not the construction itself. Pupils take turns reading the angle back on the board and the class agrees or corrects out loud.

The construct-then-measure-back loop is the point of the step: build the angle on paper, then read it back and check it matches. Revoice a good check: you built it AND you proved it. For 135°, hold the class on the count before the mark goes down; that is where the wrong-scale slip lands.

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

Before the straight-line pair, show the 60° angle sitting on a straight line and write the total 180° on the board. Ask the class to name the partner angle before anyone builds it: if the whole line is 180° and one part is 60°, what is left? Let them reason to 120° (180 − 60) rather than telling them. That is the moment the round has been building to.