Take two or three hands-up ideas, then hold the question open: can we get all three sides right at the same time? Do not reveal the arc trick yet — that is the discovery of the next step.

Work each one live on the board — do not read a script.

• Triangle 5/7/6: draw the 7 cm base first; ask why we start with the longest side. Swing the 5 cm arc from one end, the 6 cm arc from the other. The crossing point is the only place both lengths are satisfied at once.
• Bisecting the line: equal arcs from both ends cross above and below; the line joining the crossings splits it in half at a right angle.
• Bisecting the 70° angle: one arc from the vertex, then an equal arc from each crossing point; the line through the vertex is the bisector.

Hold out for the crossing points as the key idea — that is what makes it precise rather than a guess.

Model the triangle on the board first, then let pupils build it at their desks — do not ask them to draw and watch at the same moment.

Run the circle-tool in explore mode on the IWB so the arc-swing mirrors the paper work. Invite one or two pupils up to demonstrate the set-plant-rotate hold before the class draws. Then circulate as pupils draw and catch the compass slipping — the single most common slip is the point drifting mid-swing.

The two bisections are demonstrated on the board here and practised in the Class Challenge, so keep this step on the triangle only.

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.

Every pupil builds all three listed constructions on paper. Run the circle-tool construction challenges on the IWB alongside. The 90°-bisection is the investigation beat: pupils use their protractor to confirm each half is 45° — this is where the compass-precision claim gets tested against a measuring tool.

Stretch for fast finishers who are watching the board: construct an equilateral triangle (side 8 cm), predict all three angles are 60°, and be ready to explain why they must be equal.