There's no "class" to take to become a pro pilot. A program like ASA allows low-time pilots to possibly get hired by a regional airline. Generally speaking though this type of program is the exception and not the rule, so to become a "pro" you gain experience through other means, typically instructing, flying banners or sky divers. There is no clearly defined path from point A-B in an aviation career, each pilot has to blaze his/her own trail.