Chris Hedges, in his book, Empire of Illusion: The End of Literacy and the Triumph of Spectacle, writes that the language reading levels for American political speech declined from approximately 11th grade for the Lincoln-Douglas debates of 1858 to around grade 7 in the early 1990's. My impression from looking at McGuffey's readers is that 7th grade reading level in the 19th century might equal or surpass grade 11 today. This puzzles me about what Hedges reports. Would these reported reading levels be based on reading levels of 1990 and later, or would they relate to those prevalent at the time the speech was made? And how much did the reading level for a given number of years education vary over the period from 1858 to, e.g. 1990?
Hedges' report should puzzle you!
I have not read Empire of Illusion, but I can comfortably assert that Hedges' account commits a presentist fallacy. That is, he is using the contemporary metric of "reading levels" to measure 19th century literacy practices. (He should perhaps be forgiven for doing this, given the fact that he is trained as a journalist and not as a historian.)
That said, I'd like to pick through your questions here.
First, the concept of "reading levels" didn't emerge until the 1940s, following closely on the heels of the concept of "intelligence levels" that emerged in the early 20th century. In Science and Politics of IQ Leon Kamin analyzes the emergence of IQ testing as a metric for determining military draftees' mental fitness. These tests (the Alpha and Beta tests) leaned heavily on measuring how well a person could read and write. Based on how literate a test-taker was (among some other "measureables"), s/he was then sorted into an IQ bracket. How high or low a person's IQ bracket was, the logic went, also determined how high or low their reading ability was. Consequently, as vets returned from WWII, some of whom sought to take advantage of the GI Bill, schools used IQ bracket levels as a sort of shorthand for reading level, which in turn helped them to determine whether a potential student should be admitted or not.
That said, if Hedges is using the Lexile metric -- which is one of the more popular and prominent "reading level" metrics around -- then he's committing an even more egregious presentist error; the Lexile metric originiated in 1989.
Moving on, it's not wrong per se to use a contemporary metric to evaluate something like reading levels of the past, particularly if you're interested in determining how those levels might differ from era to era. So your question about how the reading levels of the mid-19th century compare to the reading levels of the late-20th/early-21st century is a fair one, and an interesting one.
And the short answer is this: the "reading levels" of the mid-19th century were higher than the "reading levels" of today. To put it more brutally: the average 7th grader in 1858 was smarter than the average 7th grader today; they could read and produce more challenging prose, were more informed on significant political matters, and were better equipped to understand challenging arguments and concepts.
But, consider a couple of things before jumping to any conclusions about how the present day stacks up against the past:
The McGuffey reader was only one of a wide variety of different readers that circulated throughout the 19th century. In Archives of Instruction Jean Carr examines dozens of different readers, producing a sort of "wide view" of the genre (she co-authors Archives with her husband Steve Carr, as well as Lucille Schultz, but Jean Carr's second chapter, "Reading School Readers," is the section of the larger book to which I am referring). What she finds is that between the various "leveled" readers (such as McGuffey's), there was almost no correspondence between levels. That is, 7th grade for McGuffey's was not similar to 7th grade in other "leveled" readers. Further, readers that had a much wider distribution (such as McGuffey's) tended to be used by teachers in ways that did not correspond with their suggested use. That is, if I used a 7th grade McGuffey reader to teach, I might not use it to teach 7th grade students.
In 1858, significantly fewer young people attended school than do now. More specifically, poor folks, girls, minorities (not just African Americans, but also Native Americans, Irish immigrants, Catholics (!), and so on) were significantly less likely to attend school than were middle-class WASP boys. And those that did attend school often had social and familial support and encouragement that the average student today does not have. The implication of this is that, as your cursory examination of the McGuffey readers shows, students in the mid-19th century might've had a higher reading level than equivalently aged students of the late-20th/early-21st centuries -- and they most certainly did -- but this is because there were significantly fewer students of the past. And these students had significantly greater access to extracurricular things that better supported their education, thus enabling them to develop a greater reading level.
I've mentioned this in another post, but it's worth repeating here: in the 19th-century, schooling (particularly schooling advanced by the Common School Movement) became very much concerned with ensuring that the rank and file US citizenry not slip into an ignorant torpor brought about by a lack of education. Nineteenth-century schooling was a citizenship project. Another aspect of this citizenship project was the press. Think of it this way: common schools taught students the basics of the Three Rs, and the press (i.e. newspapers) taught students the basics of US political life/current events.
Whereas prior to univeral education (which really wasn't universal until about the mid-20th century), political discourse (and the journalistic coverage of that discourse) really only needed to reach a handful of highly educated aristocrats, following universal education, political discourse (and the attending coverage) needed to reach everybody, regardless of education level. This meant that the language reading levels for American political speech needed to decline if that speech was going to be understood and appreciated by the rank and file citizenry.
Insofar as your final question is concerned: I have no idea. My guess is that if you were to use a contemporary reading level metric (such as Lexile), you might find that the reading levels gradually drop throughout the 19th-century until about the 1950s, then slowly start to climb again. This is just a guess though. Really, the question is an unfair one, as it is rooted in presentism.
If I can finish on a sort of editorial note: my guess is that Hedges, a journalist, longs for the days of enlightened political and journalistic discourse. I think anyone who has got a bit of schooling under their belts probably does. That said, the unfortunate truth is that you can have lofty political and journalistic discourse or you can have universally understood and appreciated political and journalistic discourse, but you probably can't have both. This is because you can have lofty literacy education or you can have universal literacy education, but you probably can't have both. And this has little to do with the abilities of the students/citizens, and much more to do with the staggering (and perhaps impossible to attain) amount of resources required to offer literacy education that was both universal and as lofty as the literacy education received by those fortunate few in the mid-19th century.
hi! if you don't get answers here, this question would be worth x-posting to /r/AskSocialScience