First, take your foam pipe insulation and cut it so that it's about 24 inches in length. This can easily be done with scissors or a serrated knife.
Your wine cork should fit right into the opening at the end of your foam tube.
Plug up one end of your tubing with your wine cork.
Tightly wrap duct tape around the tube where you've inserted your cork.
Poke toothpicks through the foam tubing, up and down the entire length (except for two inches at the opposite, open end). Try to randomly space the toothpicks, and evenly distribute them up and down the tube.
Use your scissors to trim the exposed ends of the toothpicks off so that the picks are flush with the tubing. If you're working with smaller kids, you might want to cut the toothpicks in half first so that they can insert them themselves.
Pour one tablespoon of dry rice into the open end of the foam tubing. You'll already hear the sound of "rain" as the rice falls down and hits the toothpicks on the way!
Insert your second cork into the open end of the tube, closing it up.
Wrap more duct tape tightly around the foam tube where you inserted the cork.
Continue wrapping more duct tape up and down the length of the foam tubing. Create any patterns or color combinations you like! As you go, you might need to trim any toothpicks that are still sticking out of the foam.
When your tube is totally covered, your rainstick is done! Turn it one side up, and flip it over to the other side to make the rice fall from one end to the other!