Teen Daughter 2 was an alternate on the Storm the Castle team. This is a middle school event in Science Olympiad. She got to compete in this event at one of the invitationals and really loved it.
I had hoped to provide a link to the rules for you, but Science Olympiad only puts a sample of the rules on the Internet. You have to be registered as a team in order to get the rule book.
So, here it is in a nutshell. Teams design, construct, and calibrate a trebuchet (catapult). They are not judged on their design, but on their ability to operate the trebuchet with acuracy. The team is required to keep a log and make graphs of their trial runs in preparing for this event. The graphs should show the distances the trebuchet launched a projectile in varying circumstanses, such as the size and weight of projectile. The team also needs to be prepared to answer questions about how they collected their data and used the graphs.
A cool video to watch on this topic is NOVA's Medieval Siege which is part of their Secrets of Lost Empires series.
Coming soon: Review of The Art of the Catapult