I spent five hours at L.'s school yesterday, and when I left I had a renewed respect for the teachers who spend eight+ hours there each day, and for L. (and every other kid), who spends six and a half hours at school each day. Scott and I log many, many hours at L.'s school, and we have always appreciated their open-door policy. (Related aside: In my opinion, volunteering at your child's school is THE BEST way to better understand what goes on there, who your children's friends are, and what challenges the teachers and students face every day.) But even so, spending a block of time behind elementary-school walls as a visiting parent is a little surreal and slightly mind-numbing, and I always walk out of the building feeling a bit disconnected from the outside, grown-up world. While we're in and out of L.'s school constantly, about once or twice a year we spend a big chunk of time helping out with an event. Once a year, L.'s school holds a themed science day, and for three years in a row I've volunteered to run an experiment. For two years in a row Scott and I did this experiment with the kindergarteners, taking turns to escape so we could slip away and hang out with L. for a little while. This year I put in an early request to do an experiment with the third graders, and then I spent a couple of weeks feverishly scouring the Internet for possible experiments. (Get your clicking finger ready--I'm going to throw some links at you.) I found this site, and this one, too, and spent too long watching YouTube videos about wacky and amazing science experiments. Even though I would have loved to spend an hour or so making scratch holograms with the kids, or this amazing "Disgustoscope," I knew that, realistically, I'd have to settle on something that I could squeeze into a 30-minute block of time, that would accommodate a wider range of skill sets, and that wouldn't cost too much to set up. We settled on a balloon rocket demonstration, tweaking it to account for the maturity and sophistication of third-grade budding scientists (more on that later). You can try this at home quite easily, even if you don't have your own third grader. You can easily adapt the demonstration and the experiment end of things for any age group. For L.'s class I brought along Dixie cups, which we weighted with bolts and paper clips and then attached to the balloon rockets. We tested different incline degrees, and made "boosters" out of smaller balloons to see if this would affect the speed of the rockets. You can also use paper towel tubes as boosters, or weight the balloons by inserting paper clips inside of them before the big launch. And while some of the kids enjoyed experimenting with letting the air of the balloons in such a way that they made cool farting noises, most of the kids thought the balloon rockets were the best things ever.