Cogito
Grade 1 Math · Chapter 9 · Lesson 1
What Makes a Shape a Shape?
Some things about a shape matter. Some do not.
10 problems · about 11 minutes · 1.G.A.1
What this lesson teaches
The child distinguishes defining attributes such as number of sides from non-defining attributes such as size, colour, and orientation.
- Sides and corners decide what a shape is.
- Colour, size, and turning do not decide.
- A triangle has 3 straight sides, always.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — When the Ones Make a Ten: 16 + 17 = ?
Answer 33
Why 2 tens and 13 ones becomes 3 tens and 3 ones.
Review — Adding Two-Digit Numbers: 21 + 14 = ?
Answer 35
Why 3 tens and 5 ones is 35.
Review — Word Problems Within 40: Whole 35, one part 15. Other part?
Answer 20
Why 35 − 15 = 20.
Review — Tape Diagrams for Stories: Parts of 13 and 12. What is the whole?
Answer 25
Why 13 + 12 = 25.
Warm Up
Straightforward practice. Get the method working first.
3 problemsHow many corners does a triangle have?
Answer 3
Why 3 sides make 3 corners.
Is a tiny green triangle still a triangle?
Answer Yes.
Why Size and colour never decide the shape.
How many sides does a triangle have?
Answer 3
Why Count the straight edges.
Build It Up
The same ideas with more to keep track of.
1 problemDoes turning a shape change what it is?
Answer No.
Why The sides do not change when you turn it.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsWhich one decides the shape?
Answer How many sides it has.
Why One of these can change without changing the shape.
Two Shapes: A big blue triangle and a small red one. Are both triangles?
Answer Yes. Both have 3 sides.
Why Both have 3 straight sides, so both are triangles.