This activity is perfect for K - 2. I created it for my own 1st grade class a few years ago. They LOVE to do this experiment! If you have time before hand it's always fun to dye them and draw faces on them :)
Hard boiled eggs
Sandwich size Ziploc bags
Variety of materials to fill bags with
Boil eggs prior to activity, one per student. Lay out a variety of materials for students to choose from; feathers, cotton ball, pencil shavings, sand, bubble wrap, socks, etc. Have students select one material to fill their bag with. Students make a prediction on whether their egg with crack or not. Insert egg inside of bag. Hold above head and drop.