Close to a Hundred
Four digits, two numbers. Get as close to 100 as you can.
For grown-ups
- How long: 5 to 10 minutes is plenty. Short and frequent beats long and occasional — the early-numeracy trials with the largest effects ran eight weeks or less.
- The strategy to reinforce: “Tens first” — The tens digits decide most of it. Put your big digits in the tens places, then check what the ones do. If they stall, remind them of this rather than giving the answer.
- 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.
- On the timer: it is off unless you turn it on, and it is never needed. Use it only once the skill is comfortable, never to introduce it.
- 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
Choosing where to put digits to land as close to a target as possible.
The catalogue had no target-number game, which is the format the classroom tradition singles out — the youcubed "How Close to 100?" task is the canonical version. Unlike a drill, the arithmetic here serves a decision: you cannot choose where to put a digit without estimating the total first, so place value becomes load-bearing rather than recited.
- The underlying idea
- A target-number game turns arithmetic into a decision. The child must estimate before committing, which is what makes place value matter rather than just being recited.
- Where this sits in Illustrative Mathematics
- 2nd grade Unit 1: Adding, Subtracting, and Working with Data · 2nd grade Unit 2: Adding and Subtracting within 100 · 2nd grade Unit 7: Adding and Subtracting within 1,000
- Sources
- youcubed et al. (2015) · Illustrative Mathematics / Kendall Hunt (2024) · Barton (2018) all references →
Related measured skills: CALF · Adding with carry, ALPACA · Early operations. What this means