Take three hands-up answers, not open call-outs. Give a few seconds of quiet think-time first.

Do not confirm an answer yet — the point is only to get pupils noticing that some angles are reachable and some are locked until you find another one first. Revoice a strong contribution: so we can't get that one yet because we don't know its neighbour.

• Figure 1 — angles on a line. Ask for the missing angle before revealing; hold out for 180° minus 125°, not a guess.
• Figure 2 — vertically opposite. Ask pupils to point at the angle that faces the 130° one; the two are equal, no calculation needed. Name the phrase aloud: vertically opposite angles are equal.
• Figure 3 — triangle sum. Straightforward; keep it brisk.
• Figure 4 — this is the make-or-break one. The 70° from the triangle is reused as an angle on a line. Name that out loud: we found one angle, and that angle then unlocks the next.

Talk this one through together — one pupil sets the ray at a time and the class agrees or corrects out loud. Before each reveal, put the question to the whole class and take two hands-up answers so the watching majority stays with the board across all three turns; revoice a strong answer each time.

Insist that each pupil names the fact before setting the ray: angles on a line, triangle sum, vertically opposite. The named fact is what you are grading, not just the number. The triangle's third angle is 180° − 65° − 40° = 75°.

Common slip: pupils try to name the vertically-opposite angle before they have found the line angle. Steer them back to the order — you cannot reach a later angle until its neighbour is known.

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.

The final challenge sits on its own separate straight line, drawn apart from the triangle. At one point on that line, three angles are all marked in the figure — a right-angle box (90°), an arc labelled 55°, and the blank target. Because the three together lie along the straight line they make 180°, so the missing one is 180° − 90° − 55° = 35°. None of the angles in this last part repeat a value from the triangle part, so there is nothing to confuse — point at the second line on the board so pupils see it is a fresh figure.

Insist the fact is named before the Check: two facts joined here (three angles at a point sharing a straight line, one of them a right angle). Every pupil enters at the triangle sum; the strongest stretch on the final split.