Eighth grade then would equal a master's degree today from most higher ed institutions.
If I'm remembering right, through the early to mid 19th century, grades 1 through 5 were considered primary education and were the highest learning of the average person. Grades 6-8 were "university" of a sort and it was something special that your parents would send you off to. If you graduated from the eighth grade you were a well educated person.
Our education system today could really use a massive overhaul.
Personally I'm thinking that Elementary school should be restructured as to equip people with all the basic skills they would need to be a productive person. A very good reading comprehension (because that really is the basis for all future self-education), primary math, and a good basis for the social construct of our country and it's history. If they simply can not continue on beyond this point then so be it, but they should at this point be able to find gainful employment and be able to manage their own affairs.
Junior High which should introduce some higher math, basic sciences and a more expanded history and understanding of the world in general. At this point it should be going at it as the Renaissance Ideal, a broad and general grasp of most things in order to equip the person to be able to do most anything they set themselves to.
If the person shows an aptitude for further education (lets be honest, not everyone does), then move them on to High school for the higher level sciences and arts. This should be supplemental and specific education, they should not be trying to secure basic life skills at this point, that should have been covered 8 years previously.
But, what do I know, I'm not a "professional educator" and never went to some University that costs $50,000 a year, right?