Realistic, not Idealistic
"I was being a little idealistic, and thought maybe some other objective qualification was needed, as teaching capacity and abilities"
Dr. Triax
I have worked in several ANSP's and agree with the other comments made on here that a basic 12 months qualification and an OJT course is all you need in most places to become an instructor.
That is not to say you become a good instructor, I am of the opinion that meeting minimum course and time requirements is a good start, but refresher courses, human factors courses, systems for adult learning, communication skills and most importantly, teaching abilities, should all be part of any skill set that a "good" instructor must posess.
Eurocontrol runs fantastic courses in Lux for both OJT and classroom instructional techniques, Airways runs week-long refresher courses every (5) years I think it is to keep everybody up to date with the latest training techniques and equipment.
Proper training and natural ability can make a good instructor, more
experience helps, but experience alone does not automatically make you a better instructor.