I conducted ATCO interviews for nearly 8 years, 2001-2009.
At no stage can I remember a candidate who had a degree was more favoured purely because (s)he had a degree.
It's all about how you make decisions, solve problems, change plans, cope with adversity etc.
Equally, the fact that a candidate had spent time in the air cadets or had done some flying was not held in the candidate's favour in and of itself.
If a candidate claimed to have some pre-existing interest in ATC and aviation, of course it would be beneficial to be able to demonstrate evidence for that, but it's certainly not a requirement, nor an indicator of future performance.
The candidate should certainly try to impress the interviewers in terms of how they have prepared for their interviews.
Some of my interviewer colleagues used to ask all sorts of aviation knowledge questions, inside leg measurements of 747s, that sort of thing. That can be taught. Knowing that sort of thing doesn't make you a good ATC student.
I'd far rather spend thirty minutes exploring how you as a candidate cope with a rapidly changing situation, how you prioritise information inputs, how you cope with coming across a broken traffic light stuck on red in the middle of the night.