How does one cheat at a test of this sort?

Team leaders know the question in advance. They are seperated from the team, but if they want to communicate they can.

http://www.quora.com/How-did-North-Korea-cheat-in-the-IMO-in...

Edit: have a read of this page. It shows that marking is not just a case of comparing the answer papers with a pre-prepared answer script. There is discussion and debate involved. http://www.imo-register.org.uk/2010-report.html

> Problem 4 was the second geometry problem, and so I led. We agreed four 7s straight away. The disputes were that I wanted a 7 for Luke Betts, and the co-ordinators were only offering 3 because they thought that there was a hole in his argument. On the other hand, they wanted to give Andrew Carlotti a 7 but I was only prepared to take 3. I explained to them the weakness in Carlotti’s argument, and they looked a little surprised. I asked them about the alleged weakness in Betts’s script, and I couldn’t understand what they were worried about. I suggested an overnight adjournment so that we could both make detailed preparations, and we met again the next day.

Interesting. Thanks for the response!

Just being able to communicate among the 6 participants would be enough to make a huge difference. It's like if 6 people took an SAT test together, they'd likely do better than any one could do individually.