Angles and Lines
Acute, right, obtuse — then work out the missing angle.
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
Naming angles by size, and adding angles that meet at a point or on a line.
Angle sums are among the first places a child meets an unknown that has to be deduced rather than computed, which is the beginning of algebraic reasoning rather than the end of arithmetic.
- The underlying idea
- An unknown deduced from a constraint rather than computed.
- Where this sits in Illustrative Mathematics
- 4th grade Unit 7: Angles and Angle Measurement
- Sources
- Illustrative Mathematics / Kendall Hunt (2024) all references →
Related measured skill: ALPACA · Elementary operations. What this means