FAA
Ok, here is how it works here. There are several Layers.
You need proven experience of several years or 1900 approx hours of training that is text book and hands on to recieve approval from the FAA to test for an A&P, little of this training will prepare you for the modern jet unless sheetmetal is your desire.
Most start off with an MRO or feeder earning 10-15 usd an hour (many are going to A&P school ang getting picked up by energy companies).
The feeder places allot of responsibility in the hands of a "green" AMT. You sign for your own work. The FAA has maintained a loophole that you must have performed a task supervised before doing it yourself and signing it off yourself. This is rarely enforced. The loophole is that the FAA started pushing airlines to provide atleast 40 hours of classroom training that is aircraft specific teaching each ATA.
The MRO is a Jungle of unliscenced, what you call "fitters". There is supposed to be a ratio of liscenced to unliscenced mechanics, leads and supervisors must be liscenced and the mro is often 100% "buyback". Every item requires a liscenced inspector (A&P is the only legal requirement for this type of inspector but they are usually tired old lazy bastards who don't want to get dirty anymore, got layed off from or never made it to an airline). 100% buyback allows a 145 allot of leeway with the FAA as the owner of the aircraft is responsible as well to ensure the MRO is compliant.
Career progression is usually MGT within the above mentioned or off to an airline. Airlines employ 100% liscenced AMT's, usually provide 80-160 hours minimum training on each type, recurrent training for lower landing minimum, engine run, RII etc. This is usually as good as it gets.
GA is a whole different world.