Pilates is Pilates is Pilates - Right? Well, not exactly. The Pilates method was created in the early 20th century by its namesake, Joseph Pilates. Joseph Pilates never trademarked his method, so there is quite a variety of classes taught as Pilates - some quite close to the original method and some so far removed that they really shouldn't be called Pilates.
The original students of Joseph Pilates or "elders" passed on what they had learned. The elders each had their own experience with the method as well as their own interpretation of how and what to teach. Taking what they learned and trying to improve upon it. Some changed it more then others. They each had students or "2nd generation". Some of them started their own schools as well, again making slight changes.
There are two modern schools of Pilates: Classical and Contemporary. Classical programs, such as Power Pilates, focus on preserving the exercises as Joseph Pilates taught them and in the order he taught them. There are slight variations between Classical schools as to the real version and order, but the overall method is largely the same. The sequence of the exercises beings with the client lying down where gravity can assist in gaining the connection to the core. They progress to sitting or standing during the session.
Contemporary programs vary more widely and may incorporate new exercises and variations or pull from other modalities, such as physical therapy, yoga, boxing, golf, horse back riding, and surfing.