"The juniors know less than the seniors.
"We have one boy who's playing a Nazi sympathiser who is a great historian, he has a really great knowledge of the time so he's been sharing some of his knowledge with the cast."
They had been working on the show since April, going to two rehearsals a week, as well as further sessions for specific performers.
Students had been working hard, Gregg said, and they had increased their workload recently.
"We're on day 19, I think, without a break and we're right through until production."
• There will be three shows at 7pm on Thursday (August 19), Friday (August 20) and Saturday (August 21) night this week. The show is at the school's Prince Edward Auditorium and there will be door sales. Tickets can be bought online by searching 'Cabaret' at trybooking.com.