Most of the time I give my students instructions as to how to hollow out an egg at home which they then bring into class. This blog has great, simple instructions for hollowing out an egg: How to Hollow Out an Egg
Instead of confetti, we often fill our eggs with bird seed. This way, when we break them outside, our mess becomes food for the birds! We cover the eggs with glue and then add the tissue paper. The tissue paper also helps to keep the eggs together once they are broken, which is easier to clean up.
After they are dry, a day or so later, we all go outside and sit in a circle. Students take turns walking around the circle, like in the game duck duck goose, and crack the egg on someone's head for a surprise. We discuss the original use of the cascarones, which was to show someone like that you like them.
Here is a FREE informational sheet you can share with your students to help them learn the history and current traditions associated with cascarones.