Adding to Twenty
Sums and differences to 20, starting with the easy ones.
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
Addition and subtraction facts within 20, including the ones that cross ten.
Sums within ten come first, then the sums that cross ten, then the matching subtractions. Crossing ten is the genuine step change: it is where counting on stops being efficient and a strategy (make ten, then add the rest) has to take over.
- The underlying idea
- Crossing ten is where counting on stops being efficient and a strategy must take over.
- Where this sits in Illustrative Mathematics
- 1st grade Unit 1: Adding, Subtracting, and Working with Data · 1st grade Unit 2: Addition and Subtraction Story Problems · 1st grade Unit 3: Adding and Subtracting Within 20
- Sources
- Illustrative Mathematics / Kendall Hunt (2024) · Fuchs et al. (2012) · Codding et al. (2011) · Geary (2011) all references →
Related measured skills: ARF · Addition facts, ARF · Subtraction facts, ALPACA · Early operations. What this means