As has already been said, these courses (the good ones) are a good introduction into the trade. It is now coming up to 6 years since I did mine and its only now really that I feel that I have the confidence and knowledge to tackle each and every aspect of the trade, having said that, there are still areas that I need to research and questions that I need to ask, there are always going to be scenarios that you haven't faced before. I wasn't a complete novice to tiling when I did my course, so had a bit of a head start on those who hadn't picked up a trowel before. It has been a long hard slog but I have persevered and got my business to a point now where I'm actually making a very comfortable living, don't be fooled into thinking that after the course you will be able to earn a grand a week straight away, building the business and getting contacts and a reputation to ensure you have a constant flow of work is just as hard as the tiling side. My biggest piece of advice for anyone just starting out is, use this forum, it is full of valuable information that will help you along the way, also keep up to date with materials and fixing methods, attend as many courses offered by manufacturers as you can. Never drop the ball, always strive to offer something that your competitors don't. In time all of these things will help you to become a better tiler and get you that all important reputation you will need to succeed.
I hope this gives you some idea of what can be achieved and how I have done it, I feel like I have done an apprenticeship but without the direct help of someone being with me everyday. I've made some mistakes, but learnt from them. I probably spend 2-3 hours a day on this forum reading and learning from existing posts and other members and will continue to do so for as long as this forum exists. It is a wonderful business tool and the more you put in the more you will get back, use your profile as a mini website, put pictures of your work on there and direct any potential customers to it. Never be afraid of a bit of self promotion, modesty will get you nowhere.