Remember how excited you were when you saw your first helium balloon? Until then, everything fell DOWN. But here was something surprising. Helium balloons fall UP.
Science teachers have the wonderful task of rousing their students frequently with what are known in the trade as "discrepant events." Anything that behaves in an unexpected manner, but follows scientific principles, is a discrepant event.
One of the most expensive books I bought when I began teaching chemistry was Tik Liem's book Invitations to Science Inquiry. Did you know that a full balloon weighs more than an empty one? You can make an invisible flame extinguisher with baking soda and vinegar? You can pierce a potato with a straw? And for chemists, the book provides a variety of color changing formulas that look like magic.
There are hundreds of such events, demonstrations and experiments. This book is great for home schoolers as well as teachers. And it's now available free.