Suspect many WW collectors are familiar with Venezuela's ubiquitous "escuela" (schools) issues. However, unless your focus is Venezuela, the specifics of their origin is either unknown or hazy.

The Venezuela government of the late nineteenth century was committed to expanding the availability and quality of public education. Absent a sustainable school/education financing mechanism, the Venezuelan government decided upon introduction of a "transactional" tax or fee on certain documents by requiring the purchase/use of a dedicated stamp. According to philatelic author and researcher Williams Castillo, "It didn’t take long before these stamps were being used for postal service." (Hence their inclusion in the Scott catalogue.) According to Castillo, the idea was so successful that between 1873 and 1885 the number of schools rose from 392 to 1,957.

While Castillo’s recently published book (Introducing Venezuela's 1871 - 1880 Escuelas Stamps) recognizes the eight different series of "escuelas" (released between 1871 and 1893), his considerable research focuses on the first three series (nine printings, through 1878).

Thanks to the website Classic Latin America for alerting me to this new and interesting philatelic resource.