This would be great for practicing addition skills. How to make a unique bean bag toss game from terra cotta pot saucers and a printable (which you can get for free by clicking through!) (Diy Crafts For School)
How to Make a Leak Proof Water Blob (without tape! We did a blob last year. The kids loved it. And it leaked. I looked over how she does it (iron-genius! We added glitter to our water to make it a little more fun.
How to keep a child busy for hours in the summer: DIY: Giant Ice Cube Awesomeness - filled with plastic animals, dinos, and such. And I'm sure you could put in food dye before its frozen to color it like the ice block in the photo.