Harvard University
Harvard University: The Solar System
These hands-on activities are a great way for students to gain perspective on the relative sizes and distances of each planet, the relationship between the sun and Earth, and much more.
University of California
Uc Berkeley: At Home Astronomy: The Size and Distance of Planets
In this activity, "You will investigate the concepts of relative size and distance by creating a basic model of our solar system." Planet printouts are provided and this site contains related links.