The North American Brass Band Association (NABBA) championships have a somewhat bewildering number of sections listed on their website. Bands specify when they register for the contest each year which section they want to compete in, and are generally not promoted or relegated through any official procedure. However, if a band wins their section three years in a row, they must move up a section or (if they are already in the top section) take a year off. In general, this self-selection has worked well, as bands that are unable to compete effectively and consistently at a given level find the effort unrewarding and drop down to one which is more fitting.
It is worth noting that NABBA exists not to strictly run contests, but to foster the growth of brass bands in North America. Therefore, while the main sections enforce instrumentation rules, opportunities exist for participation by bands that do not meet these standards (maybe they have some trumpets instead of cornets, or french horns instead of tenors). Also in the interests of inclusiveness, bands from abroad have been welcome to compete if they meet the membership requirements - Hawthorne City from Australia in 1994 and Stavanger from Norway in 2003 have both done so.
The sections and rough UK equivalents are indicated below.
Championship Section = Championship and high First section
Honors Section = First & Second section
Challenge Section = Third and Fourth section
Youth Section - obviously open to youth bands only
In addition, there are Open, Exhibition, and Explorer sections - I am somewhat unsure about what the differences between these classes are. I believe that Open performs the same test piece as the Challenge section, but has open instrumentation. Exhibition is non-competative, and no prizes are awarded. Explorer - I'm not sure what differentiates it from the others...
-Lothian