How to teach rounding

Grade 2 to Grade 5

Rounding replaces a number with a nearby 'friendly' number, usually the nearest ten or hundred. 47 rounds to 50; 432 rounds to 400. It powers estimation: rounding first makes mental checks quick, and it is how we sense whether an exact answer is reasonable.

How to teach it

1. Start on a number line: mark 47, then ask which ten it is closer to (40 or 50). Distance, not rules, comes first.
2. Once 'closer to' is secure, teach the digit rule: look at the digit to the right of the place you're rounding to , 5 or more rounds up, 4 or less keeps it down.
3. Practise the awkward middle case: 45 rounds UP to 50 by convention.
4. Move to hundreds and thousands only when tens are automatic.
5. Use it for real: estimate shopping totals or sums (298 + 51 is about 300 + 50).

Common mistakes

• Rounding the wrong digit (looking at the tens when rounding to the nearest hundred).
• Changing digits to the left as well as the right (473 to the nearest ten is 470, not 500).
• Thinking 45 can round down , by convention 5 always rounds up.
• Rounding after calculating instead of before, when the point is estimating.