Aptitude should be something inherent (i.e born with). No one is born to be a Controller, but you may have the "talent" for it and find it easier to learn and master the necessary skills (like many jobs actually?)
Some aptitude tests can become easier when repeated (familiarisation & learnt mistakes), so testers will often only allow candidates a small number of attempts.
I was told by my training officer he'd rather have a student who was a keen canoeist than a rock climber - His rationale... a canoeist is presented with a hazardous situation where he has to make a snap decision and work his/her way out of the problem; whilst the rock climber in a harzardous situation can take time out, cling/tie themselves onto the rock face whilst working out the safest path to the top. Not very scientific (and for all you ATCO mountaineers sorry, but I used to own a kayak) I'm not sure I completely agree with this a selection criteria, but can see where the idea came from?