Fold a real or projected paper heart down the middle so the class sees the two halves land together. Then hold up a square. Take two or three hands-up answers on where a square could fold; do not confirm or correct yet, just collect predictions to test in the next step.

Display mode: you drag the mirror line, pupils only watch. Before revealing each shape, hands-up: how many matching folds? Take two answers so the room stays with all four, not just the rectangle.

Square: side-to-side, top-to-bottom, and both diagonals all match. Four lines.

Rectangle: two straight-across folds match; pause on the diagonal and let them predict before showing the halves miss. Two lines.

Letter X: vertical matches, horizontal matches. Two lines.

Letter T: only the vertical fold matches. One line.

Keep pressing the contrast: the square's diagonals work, the rectangle's do not.

This round is for talking it through together — pupils take turns at the board and the class agrees or corrects out loud.

Name a shape, then send one pupil up to drag the mirror line and test it. Ask the class did the halves match? before confirming. Watch for the common slip on the rectangle: pupils try a diagonal fold expecting it to work like the square's. Revoice: so the diagonal works on a square but misses on a rectangle. Rotate four pupils across the four shapes.

These are the practice questions — 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 letter S is the trap: it looks balanced but no fold makes its halves match, so the answer is zero lines of symmetry. Let pupils try a fold and discover the miss rather than telling them. Revoice the big idea: looking balanced is not the same as having a line of symmetry. Press the Check button after each pupil sets their lines.