There were a number of reasons for this. Yes, they turned up smart and well prepared for the assessment centre, and (mostly) on time. They got stuck into the tasks in the group exercise, worked well with their fellow candidates, and had good examples ready to talk about during the interview. But one thing in particular stood out: a really strong sense of pride in their achievements.
All of our successful candidates were able to demonstrate this by being passionate about the examples they described in the interview. That is why they were successful, and will be helping to represent City over the next 12 months by meeting young people from disadvantaged backgrounds as part of our Outreach activities.
The same thing applies to any interview you go to. Identify the things that you are really passionate about, and the achievements that make you feel proud. Work out how they relate to the job you are going for. And then make sure that pride and passion shines through in the interview.