We were given this as a gift from a friend of ours and it became a huge sourse of fascination and entertainment for my sons. The gears, which are all different colors but primarily are the same size and shap, are interchangable. I would watch my sons take out one cog which would then stop other cogs from spinning and it was hugely mezmorising for them. They obviously worked out that one gear needs another gear to rotate - it doesn't just happen. I was initially worried that their little fingers would get stuck in the rotating gears but they stop turning ever so gently if something gets in the way. There are no small pieces so it is really great for any age. As they got older I would watch them put little toys or action figures in the middle of the cogs and they would laugh as they all turned round in different directions. This was such simple fun but they played with it for years. If I had to be critical, it bothers me somewhat that Playschool is spelt incorrectly, especially at a time when the children may be learning to spell.