While planet size is out-of-whack in textbooks, it's nothing compared to the distances between planets. Most textbook pictures look a little something like my picture above (except, of course, the planets all look much closer in size), the planets are all right next to each other. The textbooks do it for the same reason that I did: it's the way to make all the planets fit.
There's so much empty space in space that it's darn near impossible to show students both the planets and their orbits to scale.
But, if you want to give it a shot, pick up your props from last week's solar system and head out for a walk....
Start at the sun and walk 190 feet. Place the peppercorn (Mercury).
Walk 170 feet. Place the mini-marshmallow (Venus).
Walk 131 feet. Place the Gobstopper (Earth).
Walk 263 feet. Place the split pea (Mars).
Walk 601 yards (about 1/3 mile). Place the soccer ball (Jupiter).
Walk 1/3 mile. Place the melon (Saturn).
Walk 1 mile. Place the baseball (Uranus).
Walk 1 mile. Place the small apple (Neptune).
Walk 1 mile. Place the sprinkle (Pluto).
You've walked more than 3 1/2 miles from the sun to get to that tiny sprinkle of Pluto. How much sun do you think Pluto sees? Not much!
Given that you probably don't want to walk your students out 3 1/2 miles (and then back 3 1/2 miles), you might want to have them walk the first 190 feet, to get an idea of the distance. And, then you could determine where each of the other planets would fall, within your school and community. For example, the Earth is at the cafeteria, or Uranus is at McDonalds.
It's completely mind-boggling and a lot to think about!