Break it down to amateur parts changer's, then gunsmith's that are going to run machinery to work on the firearms to customize/repair  them.

So not only may you be working a gun that costs in the 10's of thousands of dollars to replace if you screw it up, but working a machinery that you can do that much damage to the machine in less than a minute as well.

Bluntly, most of your time starting off in a technical school will be learning first how to run the machinery without crashing it or destroying the work piece to being with, then how to use these skill to gunsmith afterwards.

Let the first page scroll through the photos on top, and you get a feel for the classroom/where you are going to spend most of your time just to learn how to use these tool correctly (so you don't crash them, or kill yourself instead).
http://www.schooloftrades.edu/

And to prove this point, lets start out with a easy one, being a revolver that has too much BC gap.

Barrel and cylinder need to be removed from frame.  
Cylinder may need to be faced to remove pitting, so we begin by facing the cylinder.
Next is the barrel and its shoulder need to be faces so it can be threaded into the frame at least one wind, it not two winds more (depending on the amount that the cylinder had to be faced) and correctly index to the frame when the barrel is reinstalled to the frame. Now with cylinder back together and back in the frame for measurements, the breach face of the barrel needs to be faced to achieve a .006" BC gap when installed  correctly, and the forcing cone re-tapered as well.

Granted that there is much more to a revolver rebuild/BC gap correction but, as you see, this is a high machining job, with little to no parts being replaced with new parts, hence no amateur drop in parts changing.

School, then experience.  You'll damn near have to make it your life to have success.

Formal training provides concentrated experience on the spectrum of topics under guidance of experience, so a person has a chance to be productive in the shortest possible time, but not necessarily a master of the skills.

The same goal can be reached with lots more time, blind alleys, money, and ruined or half assed work.  Some customers will give you a shot at work, because your prices will be low.  You will have to carefully build a reputation no matter which path you take.  

Another approach is to do only work on speculation, in other words, no customer or commission work; if you're good enough, you'll have no problem selling your work, and if your work is sufficiently high end, it will bring high end prices from wealthy people that have a hard time finding what they want to buy.

The summer courses via the NRA program are a bargain.  http://www.nragunsmithing.com/.  I have been to two of the schools.

Another source of training are classes at Connor Prairie and Western Kentucky University.  These short term classes are aimed at building of American longrifles, but the skills are transferable to any firearm work.

I know of two gunsmiths I should send you to visit.  

One is in Silex, Missouri; that is the one you should emulate.  He runs a business, does good work, and turns it around in a timely manner.  BS time in his retail shop is Saturday morning.

The other one is in Choutea, Oklahoma, and although the guy knows what he's doing, he ain't doing it in any hurry and he has dozens and maybe hundreds of guns backlogged, but he likes to hold court in his shop.  His shop is a piled up mess, and while it's fun to visit, I wouldn't snd a gun there.

One other thing to consider is the sheer number of gunshops in Missouri.  They're everywhere these days.