Give five seconds of quiet think-time, then take two or three hands-up answers. Listen for pupils saying below zero or below freezing rather than just very cold.

First line, markers at −8, 0, +6. Point to each, say its distance from zero: eight left, six right. Stress zero is the middle, negatives left, positives right.

Lift: carpark −3, ground 0, top +9. Trace finger up so class sees it pass through zero.

Birr fall: +2 in afternoon, −5 overnight. This is the make-or-break idea. Count aloud: 2 down to zero, then 5 more. Pause before the total, let a pupil say 7. It's 7 because the change crosses zero.

Build the rule for the Class Challenge. Opposite sides of zero: count both parts and add, 2 plus 5 makes 7. Same side, no crossing: count within that side, e.g. −8 to −5 is only 3 steps. Point to the line for each case. The decision that matters is whether the change crosses zero.

This round is for talking it through together. Watching pupils show a thumb (left or right) as their whole-class prediction before each named pupil places a marker, so the back rows stay with every placement.

Have four pupils come up in turn to place −6, −9, +4 and 0. Watch for the common slip of thinking −9 is smaller so it goes closer to zero — it is actually further left because it is further below zero. Revoice a good answer: so the bigger the digit after the minus sign, the further left it sits.

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 key discrimination is the first problem versus the rest: −16 to −19 stays entirely below zero, so it is a simple 3-degree drop (count within the negatives), whereas the others cross zero and need the two parts added. The stretch crosses zero the other way — the temperature rises from −4 up through zero to +3, which is still 4 up to zero plus 3 more above, a 7-degree change. Revoice: rising or falling, if it crosses zero we add the two parts.