Turtle Graphics comprise Move and Turn commands which allow the child to move the sprite around the screen with simple control commands. These commands are an important way of introducing children to geometry when combined with the pen commands that leave a trail as the sprite moves. The idea is that the children can experiment themselves and discover how to draw a triangle, square, pentagon, and other shapes without necessarily knowing the angle required to draw each shape. This is an important principle of ‘constructivist’ learning that forms part of the power of the LOGO language used in education over the past thirty years. Scratch provides an easy way of getting children to use turtle graphics without the need for a physical robot.
Scratch provides the Move and Turn motion command blocks to move and turn the sprite. The lesson involves the children moving a sprite (which they might have drawn themselves) around the screen by selecting and clicking on the appropriate command blocks once they have dragged them over to the script area in Scratch. They can join blocks together and use the pen commands to draw shapes on the screen. By the end of the session they should be able to draw a triangle and a square and put sequences of commands together to draw more complex shapes.
The video shows many examples of turtle graphics including squirals, and stars, and flowers, as well as the standard polygon drawing techniques. The children learn for themselves during the session that a 90 degree turn is a corner that can be used to draw a square. For younger children it is best to let them always use the same angle for turning (say 30 degrees) and discover that three turns is required for a square and four for a triangle. If they have experienced one key logo before this session, turtle graphics will be easy for them.