#### Material

The triangles correspond to those in Box 1. (one of each type)

They are blue with no black lines.

1 pair right-angled isosceles triangles.

1 pair right-angled scalene triangles.

1 pair equilateral triangles.

1 right-angled scalene triangle.

1 obtuse-angled scalene triangle.

#### Presentation

- Invite the child to the lesson.
- Take out a triangle and place it on the rug.
- Take out its corresponding triangle and place it next to the other one.
- Place one triangle on top of the other one.
- Take a moment to examine their size.
- Take the triangle off and place it back next to the other one.
- Bring the pair together.
- Hold a triangle still with your left hand.
- With your right hand on the other triangle, slowly slide the triangle clockwise along the edge until two points meet.
- With your right hand, slide the triangle to the right.
- Examine the new shape that was formed.
- Ask the child if he knows the name of the shape.
- Slowly slide the triangle along the edge until two new points meet.
- Slide the triangle up along the edge.
- Examine the new shape that was formed.
- Slowly slide the triangle up along the edge until two new points meet.
- Slide the triangle to the left.
- Slide the triangle down, forming its original shape.
- Invite the child to remove one new pair of triangles, until he has worked with them all.

#### Exercises

Exercise 1: Child works independently.

Exercise 2: Flip Over*Flip over one triangle of each pair and let the child explore them.*

#### Language

None.

#### Control of Error

None.

#### Direct Purpose

To show the child that joining two triangles forms a single straight lined figure.

#### Indirect Purpose

Preparation for understanding equivalence.

To see how all plain geometric figures constructed of straight lines are composed of triangles.

#### Age

4 to 5

#### Notes

Same shapes as in Box 1, except they are all blue and have no black lines.

We are gradually moving towards an understanding of equivalence.