How do you make a pulley project for a third grade child?

Ooo,...this sound like it would be fun! Well probably one of the most interesting things about pullys is that if the pully is on the movable part of the line it provides you with a mechanical advantage of 50%! That is to say, properly set up you can lift a 10 pound weight with just 5 pounds of force. If the pully isn't moveable it only provides a fixed point from which to change the direction of pull and no mechanical advantage at all! In this it take 10 lbs of force to move a 10 lb weight. This should be pretty easy to show a 3rd grader and fun too!