It depends on your definition of eigth grade. Here's the 8th Grade Final Exam: Salina, KS - 1895. Take a guess how well the average 2003 8th Grader would do.
I have a copy of the original "McGuffey's Readers" that were used in the "Little House on the Prairie" one-room schools in the 1800's. Here's a selection from the Fourth Reader:
...There is a lowering sublimity in his brows, which one seldom sees equaled, and the obliquity of the light shows the upper and lateral parts of his forehead, proud and palpable as the hills of his native north...The above is an example of 6th-7th Grade reading level of the 1800's.
The definition of 8th grade is now "what is within the ability of a bottom-20% kid to learn in 8 years". Define the bar low enough, and yes, just about every kid can make it. Just about every kid can learn to play basketball, too. More or less. But add the requirement: "Play well enough to make the Varsity team", and it's a whole different story.
What would a high school education be, if "high school educational load" was defined as "that amount of learning which would strain the intellectual ability of a teen in the top 20% of intellectual ability"? That is what high school USED to be in the 1800's: you either maintained the pace, or you dropped out.
My kid is gonna hate you. I printed that and will work it into the lesson plan. :)
The biggest problem with educating children is failing to realize how smart they really are. Your example from McGuffey's Readers illustrates that point perfectly. Children will respond in a manner that reflects the person addressing them. If you say, "Yo! Kid! Knock dat sh!t off! I'm watchin' Sex n da City," the kid is likely to respond, "Awww %*$*! you." If you tell the kid, "Please turn that down," the kid will probably say, "Awww! Do I haaaaave to?" To which the wise adult will respond, "Yes, or I will make you learn calligraphy ("once you are capable of sitting again" -- this part is optional)."
I never quite got the "baby talk" thing -- I was never very good at it. So I didn't do it. As a result, my son had a large vocabulary for a three year old ("Mama, I am not 'noxious.") This didn't play well once he got into school. Some of his teachers thought he was making fun of them (he did think one in particular was a little "slow").
I'm fortunate that I have the luxury of homeschooling, and my son still has a killer vocabulary (we work on colloquialisms as well -- I don't want him sounding like Niles Crane).
Several of the teachers my son had problems with had a habit of "talking down" to their students. Perhaps they felt they needed to teach to the lowest common denominator in order to be sure no one felt left out. But I found that, if a child doesn't understand you, you'll see it on his face. Instead of asking, "Do you know what I mean," I usually paraphrase and repeat the sentence until the light goes on. It usually clicks by the third definition.
I know teachers have a busy schedule, largely due to government mandates, and may not have the time to explain a lesson more than once. More's the pity. Children will rise to the level of your expectations with just a bit of help.