As Don said, these “schools” are names invented by collectors and students to classify rifles or guns by where they were made. Often, 60% or more of Golden Age rifles from an area will share a number of architectural and decorative characteristics. For a recognizable style to emerge, it seems there would have to be a dominant maker early on who influenced others by training them or by market pressure; customers wanting guns that "look like his". That means stability is part of the picture; perhaps a gunsmith established a first shop in an area, developed a style and a market, and then trained others. If on the other hand a group of gunsmiths all started up shop at the same time, a regional style may not emerge.
What can be confusing for students is the amount of variation of longrifles produced by gunsmiths within an area. So for example, we know what a Lancaster style rifle should look like, but will put a Valentine Fondersmith rifle, a John Newcomer rifle, an Isaac Haines rifle, a Dickert rifle and a Fordney rifle all in the Lancaster school because they were all made in Lancaster. Although they may share furniture (available locally or perhaps cast by a local gunsmith) and some overall architectural features, carving details and patchbox stylings will often be quite different on guns by these Lancaster smiths. Later on, there was more homogeneity as perhaps customers expected a Lancaster rifle to have a daisy patchbox. But there were still later makers with truly distinctive styles; Fordney being an outstanding example.
Same is true among Reading rifles; we'll lump a Bonewitz with a Schreit and RCA 21 because they were all made in a given region. These 3 look no more alike to me than lumping a J.P. Beck with a Dickert and a Schroyer. So in my mind there are rifles assigned to schools because of where they were made, and others that truly belong together because of shared stylistic motifs.
