Of the 36 people that started my course, 12 are not working as ATCOs. All but two of them still have a job with the company in one form or another, be it as assistants or in non-ops jobs. One of those two left to be a pilot.
Of the remaining 24, not all of us are valid 3 1/2 years or so down the line, a few people didn't make it through the college first time round and so had to wait a bit longer before starting training at their unit. A couple of those 24 have been removed from training at their unit and offered another unit.
As others have said, if you have the commitment and really want to be an ATCO, then you should be alright. Keep your head down and work hard and take on board any advice you get given regarding the practical side of things.