...was usually not going to school by the sixth grade.

Most kids didn't get that much education in 1918, so we're talking about the really motivated, the gifted, and the kids whose families could afford to keep them in school and out of the work force. The average 12-year-old was apprencticed, or working in the streets or in the family shop or on the farm, and not in school. We are looking at curriculum for the creme de la creme of the working class. The upper class were, of course, going to boarding schools intended to prepare them for Princeton, Yale and Harvard. If a girl was lucky, she got to go to the Emma Willard School, or another boarding school for young ladies on the Emma Willard model intended to provide some higher education for girls.

I remember school books in sixth grade at about this level. We used to read Hawthorne and Irving in English class. Catholic school, though, so there were other problems: I had to go to the public library for history books that depicted Protestant monarchs without fangs, and then we'd have arguments in the classroom about reading things without the imprimatur from the archbishop in them.

My grandfather worked on the railroads as a youth, but he knew how to read. Newspapers were written at a 6th grade level, specifically to allow intelligent working class kids to keep up, and to allow those who had to leave school before the 6th grade to develop and maintain their reading ability.

Part of the aim of education policy in the late 19th century was to keep the street kids in check by teaching them "appropriate behavior" and to assimilate the great waves of immigrants from southern and eastern Europe. Literacy advocates worked hand in glove with newspaper publishers and publishers of dime novels and penny dreadfuls, who had everything to gain in sales from a literate workforce.

It runs in waves. The people who had the "hard" stuff seek to make things less rigid. (Other social conditions intervene, too -- like the Great Depression.) Content is usually sacrificed as part of the relaxation. The content is rediscovered, with the cries of "Oh woe, how stupid we have become!", and things get tightened up again.

Meanwhile, the kids are all right. They are just as smart as they ever were, but they know more about the new things that come up, and less about the traditional technologies. (This was always true. Guess who were the first to love telephones and radio in civilian culture?) Expanding vocab would be useful, but you would be surprised how many words kids use when they talk but that they don't write. Writing is the eroding skill. All that takes is exposure to writing in a format that kids find hip and attractive to read. Ebooks, anyone?