If you don't work for a shop, they don't let you take the class and there is some justification for this.
You read the manual and complete a workbook prior to class and then learn some basics and get updated on the latest regs at the seminar. But (theoretically) most of the real learning will be hands on in the shop under the guidance of a more experienced tech. You then have to attend a 2 day seminar on an annual basis to maintain your currency.
Personally, if I were king of a dive equipment company, I would allow dealers to offer regulator specific certification classes to certify divers to work on their own regs. I would then allow divers, with proper repair certification and tools, to buy annual service parts through the dealer as long as they do not buy more than one kit per year per regulator and return the used parts to the dealer.
This would create another source of cash flow for the dealer, would improve diver knowledge, satisfy divers who wish to do their own maintainence without exposing the company to excessive liability, and would maintain parts control to prevent untrained diver/technicians from servicing their own regs and having their widows sue the company when they get it wrong and drown.