A week before filming began, Johannes Roberts' 1st Assistant Director James Nunn spotted some local kids practicing parkour, or free-running. They were quickly hired for the film.
At one point, this was going to be a UK/ US co-production with a considerably larger budget. However, Johannes Roberts turned the US money down in order to retain personal control over his project.
Johannes Roberts was in between projects when he found himself lecturing at the school where he ended up making the film. Upon arriving at the school, he mused that this would make a great location.
Shot in the height of summer at night, meaning that filming couldn't commence until about 10 at night and would have to finish about 3 or 4 in the morning.