For the musically inclined, have your students create noisy rattles by filling recycled containers with unpopped popcorn. Let each student select and bring in a container for the project, encourage students to think creatively about different materials, from aluminum cans to plastic bottles to cardboard tubes. Have students experiment with the sounds that the popcorn makes, depending on how much they fill up their containers. To wrap up the project, provide paper, markers and rolls of clear packaging tape so that they students can decorate the outsides of their new percussion instruments.
For jewelry that's both eye-catching and edible, have students string popped popcorn onto colorful thread to make necklaces. If you'd rather focus the project on a holiday decor instead of jewelry, you could use the same process to make long streamers, simply using longer lengths of thread and not looping their ends together. For variation, alternate the popcorn with other items, like cranberries, dried fruit or orange peels. The combination makes a particularly appropriate decoration for the autumn.
Explain to your fourth graders that popcorn "pops" because it contains a small amount of water and, when heated, that water expands to give off a sudden burst of steam. To demonstrate this explanation, subject unpopped kernels to a variety of treatments. You might let one batch of kernels sit in an oven at a low temperature for a couple hours. Soak another batch in water. Pierce another batch of kernels with a pushpin. Try popping each of the batches and see if they pop correctly. Have the students write up their interpretations why the batches did or didn't pop.
Have students guess whether different types of popcorn are better or worse at popping. For example, they could compare various brands' popcorn, buttered popcorn, all-natural popcorn, microwave popcorn and loose (or "stovetop") popcorn. After students have made their hypotheses, measure out 100 kernels of each type of popcorn and pop them under the same cooking conditions. Have students count the popped kernels and create graphs to demonstrate the results. If students can determine any possible relationships between different types of popcorn, let them do a more thorough follow-up study, using greater numbers of kernels.