SE 3.07Constructive Triangles: Triangular Box

1. 1

   Take out the triangles and sort them by color on the table.

2. 2

   Place the gray triangle at the top and point out that it has no black lines.

3. 3

   Take the two triangles of the next color, find the black lines, and slide them together until the lines meet.

4. 4

   Lay the finished triangle beside the gray one and look at both.

5. 5

   Build the next triangle from three pieces, then the last from four pieces, the same way.

6. 6

   Place each built triangle on top of the gray one to show they are all the same size.

7. 7

   Return the triangles to the box and invite the child.

What catches the child’s eye

• Four small triangles becoming one large triangle the same size as the gray one
• The upside-down triangle that fills the middle of the four-piece triangle

Extensions, easiest to hardest

1. Count the pieces in each triangle: one, two, three, four.
2. Use the pieces to build other shapes, such as a rhombus or a trapezoid.
3. Draw the built triangles and color each part.