Activity Four:
Concept Application: One to One Correspondence of Objects
Grade Level Content: 3-4
Processes: Observing, Communicating, 
Comparing, Organizing
Developmental Stages: Sensory Motor, Pre-Conceptual, Intuitive, 
Using different units for measuring (plastic links, large or small paper clips, unit blocks, Unifix cubes, rulers, tape measures, string),  measure the circumference of different balls.

Have students select a ball to represent the Earth. Then have them select different balls to represent the different planets. Remind them that the balls for the different planets must be relative in size to the one that they choose to be the Earth. Start the discussion with this question: 

"What do we know about the size of the Earth as compared to the other planets?" 
Balls that can be used: basketball, volleyball, soccer ball, baseball, ping pong ball, golf ball, marble, pea, etc.
Activity 4 Worksheet
Activity 4 Student Task Card
Planet Information Sheet