Ever played with these?
If you're not familiar with them, they're Magic Grow Capsules. They are small sponge shapes compressed and enclosed in a capsule that dissolves in warm water. Look for them in the dollar section of your favorite retailer, or in the party favor area.
They're fun! And what better way to get your students interested in the scientific method than with something fun?
There are several ways you can go with these guys.
One simple variable to test is the water temperature. The instructions say to use warm water. How long does it take for them to open in warm water, cold water and hot water? A graph comparing the results would probably be appropriate.
Is water the only liquid that works? Try out some other liquids and see if they are equally effective (make sure your liquids are all at the same temperature... you only want to test one variable at a time).
Ask your students to generate other ideas... they will...
-do they still work if the capsules have been microwaved?
-will they work in cold water in the bell jar (air pressure removed)?
-will they work if I bury them in the ground and pour water over them?