Round and Reckon
Round it first, then work it out. Does your answer look right?
For grown-ups
- How long: 10 to 15 minutes is plenty. Short and frequent beats long and occasional — the early-numeracy trials with the largest effects ran eight weeks or less.
- When they get one wrong: the page shows the working. Read it together rather than moving straight on. Feedback that explains is worth several times more than feedback that only marks right or wrong, and that gap is wider in maths than in any other subject.
- Not timed: thinking time is the point of a book. Let silences run.
- Print it too: doing the same problems on paper a few days later is worth more than doing twice as many today.
What this practises
Rounding to the nearest ten and hundred, and using it to check whether an answer is sensible.
Rounding is usually taught as a rule to follow and then never used. Here every rounding page is followed by a page that uses it to sanity-check a real calculation, which is the only reason estimation is worth knowing. It also leans on the number line: rounding is asking which ten or hundred a number is nearer to, which is a magnitude judgement, not a digit rule.
- The underlying idea
- Rounding is estimation with a rule, and estimation is what lets a child notice their own wrong answer.
- Where this sits in Illustrative Mathematics
- 3rd grade Unit 3: Wrapping Up Addition and Subtraction Within 1,000
- Sources
- Illustrative Mathematics / Kendall Hunt (2024) · Institute of Education Sciences / What Works Clearinghouse (2021) · Schneider et al. (2018) all references →
Related measured skills: ALPACA · Elementary operations, CALF · Adding with carry. What this means