How do you stack up?

For Christmas Mamaw bought Little Miss a plastic stacking toy. She loved it and worked really hard to figure out how to stack them on the center stem. Eventually it got too easy for her. I recently put that toy away and brought out a more difficult stacking toy. This one has smaller holes and the stem is straight, which isn't as forgiving of putting the discs on at an angle. My precious girl kept trying, but this toy proved difficult. The thinking tongue often came out, discs often got handed to me to do, and there was often a lot of discussion about the best way to approach the task. Just recently Little Miss seems to have gotten it. She learned to put her finger on the stem and slide the disc down around it. It works like a charm. She now will casually walk by and put on a few before sauntering off again. I also like that it doesn't matter what size she puts on first- they all stack. I'm not sure how to make this game more difficult again, but it was fun watching her master it once I raised the stakes.