I had a similar contest in school where I used a trick that I had learned just by goofing around with paper planes as a kid... You take the classic paper airpl

I had a similar contest in school where I used a trick that I had learned just by goofing around with paper planes as a kid... You take the classic paper airplane fold and simply do a double inner fold... so crease in 2x before building the wings. You basically end up with a dart that can easily fly across a gymnasium and farther depending on how hard it's hurled. I remember some kid using that design and flying it pretty far, but my darts (er, planes) were hitting high on the back wall of the gym with plenty of distance to go.