Take three hands-up answers, not open call-outs. Don't resolve the start question yet — let the disagreement sit. The 'start from the units' rule is the pay-off of the next step, so resist confirming it here.

Walk each example aloud, one at a time, working right to left.

• 4,738 + 2,569 — point to the units: 8 plus 9 is 17, write the 7, carry the 1. Build the 'why it moves left' on the board: if you have base-ten blocks, lay out 17 unit cubes, trade ten of them for one ten-rod, and slide that rod into the tens column — the small carry-1 is just that trade written down. (No blocks? Draw ten dots, ring them, and move the ring one column left.) Three regroups happen here; make pupils name each one.
• 9,876 + 1,234 — this is the real cascade. The carry into the thousands tips it past nine, so a brand-new ten-thousands digit appears (11,110). Ask 'how many carries did we count?' before revealing.
• 5,000 + 4,999 — this is the near-miss, not a cascade: it has no carries and stays at four digits (9,999). Pause on the prediction before checking; the guess of ten thousand is the slip that catches people out.

Between the first and second examples, do a quick turn-and-name: ask one pupil to say where the carry went and why, then revoice it for the room before moving on. This keeps the back rows with you across all three demos.

The single idea to drive home: a carry always moves one column LEFT, because ten in a column is worth one in the column above it.

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

Step the algorithm column by column. As you reach each column, ask the class to predict the digit and the carry before it lands. Have individual pupils come up to set each column. Watch for the common slip of writing the full two-digit sum in a column instead of carrying — say the carry out loud every time: '13 — write the 3, carry the 1'. The answer is 10,803, so this one grows a fifth digit; flag that as it happens.

This round is the practice bank — 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 first sum is a quick win so every pupil enters. The next three need real working time: 9,876 + 1,234 is the cascade into a new digit, and 5,000 + 4,999 is the near-miss — let pupils predict whether it reaches ten thousand before checking. Use the on-screen Check (✓) as part of the narration: 'yes — that's it'. Fast finishers watch the board and mouth the next carry rather than working ahead.

Keep this brief. The cascade idea (one carry triggering another) is the piece worth restating, as it is the part pupils most often forget on paper.