A balance scale stimulates children's curiosity of measuring objects. They will naturally learn what objects are heavy or light. Also, through trial and error children will teach themselves about the balance relationships between different sizes and weights of objects.
Sue has gotten us a lot of wonderful, new, indoor gym equipment, but at this time of the year, I can't help but "Think Spring". Wouldn't it be fun to build something like this to put in the grass at the far side of the playground?!