You asked a number of questions.
I set one up a Garand course once.
1. you have to supply a firearm to someone who doesn't have the model upon which you are working.
2. you start with disassembly. You take a part off and then put it back on. The student then does it. Then you take off the first part and a second part and put them back on. Then the student does it. By the time you get to the end, the student knows how to take the firearm apart and put it back together.
3. then, you progress to describing a common problem. If you can illustrate a failure or a broken or worn part, it is displayed. Then the student recites how to correct the error.
Yes, I know courses wherein people actually construct a firearm. The problem is that the machining equipment is limited and the skills vary greatly.
Most of the armorer's course would be directed at disassembly, assembly and understanding the sources of malfunction and which parts are associated. Sure, you can demonstrate how to tune an extractor. Then again, if each student is going to do it, you have to have a firearm for each student and it will be tuned to the specific firearm.