Going back a few years admittedly but back in the late '60s, I joined NATCS (as it was called then) as an Air Traffic Control Assistant, the educational requirement beng a minimum of 4 GCE (NOT GCSE) 'O' levels. To join direct as an ATCO Cadet required at least 2 'A' levels in addition to another 3 'O' levels (I actually got 6 'O' levels and one 'A' level when I left school) but I was happy to start at the bottom. I spent two and a half years as an assistant before passing the selection for ATCO Cadet but in that time I accrued a vast amount of knowledge and experience which all went towards me passing the 3 year course which involved achieving all ratings (in present terms ADV, ADI, APP, APS, ACP, ACS) and training at places as far apart as Bournemouth (the College of Air Traffic Control) and the Shetland Islands.
I saw many ATCAs who got impatient at the apparent slowness of gaining this experience and who left after as little as 3 months to pursue other professions - their loss; if you stuck at it the rewards were fantastic.