Many martial artists use the categories of “old school” and “new school” to build themselves up, and put others down. It is usually the people who are putting the others down who will label themselves as “old school”.

Another term used frequently in putting down a martial arts school is “McDojo” or “McKwoon” or “McDojang”. These terms, obviously, are calling some of the martial arts taught out there a type of “fast food”.

I have trained in both an authentic “old school”, and a by gosh “McDojang”. I would like to take a moment to list that plusses of “Old School”, in my opinion.

The old school martial art training has the following benefits;
Tough training produces really tough martial artists. It is this fact which jumps to the front of my mind when I decide to compile a list like this one. The training is tough as shoe leather, and produces an exponent in like manner. The concept of “tough training” varies style by style, but, speaking for Hung Gar (if I may be so bold), tough training can include, without being limited to, stance training, done either in a static, or dynamic manner, smashing of the limbs against various objects, typically another human, etc.
Smaller classes, which enable the instructor to give you, not only more attention, but often better attention. In a large “McDojo”, you are one face in a hundred or more, and while the instructors are taught (yes taught) to make you feel like you received individual attention in each and every class you visit, when examined, the in class attention will not amount to more than about one minute per week, if you are lucky. In the old school system you receive real one on one attention, because there are not many other people to draw attention away form you.
Very often, your instructor will have, in the old school, a better, or deeper skill level. This is not really the fault of the new school instructor – often they were never trained by someone with this deep level of skill, and so haven’t the foggiest idea how to pass it on (sometimes even that it exists). In the old school setting, you will find the instructor has time spend on their own training, whereas in new school, the instructor has to devote his spare time to business matters. This really prevents personal improvement.
Your old school instructor will typically have a deeper understanding of the system he teaches. I follow a distinction which I first heard stated by Sifu Graham Players. He drew a line between a style and a system. The system is all that underlies the individual techniques of any particular style. If your Sifu understands the system, then you will be more capable of using your martial art to defend yourself.

These are just my thoughts on the subject. Keep in mind my bias. I have trained in both, but try to teach according to my old school background.
There is, however, the fact that the “McDojo’s” make a lot more money. This is due to the fact that training old school is exceedingly hard! You must want to be old school if you will ever hope to be old school. You will pay for it in more than just money. You will pay for it in sweat, sometimes blood, and always in pain. If you are true old school, something will always hurt. You will come to regard any day as good when your aches are all minor. In later years, you will help your doctor pay his kids college tuition.

I trained in often insane ways. We used to do throws, rolls and sweeps on a garage floor. And somehow, we thought that cardboard was enough padding! We would practice countless techniques on each other, often laughing to mask the pain.

If you choose old school, be sure it is what you really want.