ZAM wrote: <<I know that im probably incredibly naive, but why do people get 'chopped' when there is a self proclaimed shortage of people in the profession?>>
Simple. People get "chopped" because they cannot do the job! ATC is a skilled job and, despite all the lead-up training, one does not know if a particular individual will be able to do the job until he/she starts live training. The ATC Licence, Ratings and Validations are all standards which have to be achieved with a high pass mark and to become fully operational the controller has to achieve all three. If he/she doesn't - "chop"!
Do note that although a controller may fail to reach validation standard at a particular unit or position he may well go on to validate elsewhere so a high failure rate at one unit does not necessarily mean that the talent will be wasted.