"it is generally accepted that literacy rates in the United States were quite high before compulsory schooling was mandated starting in the 1840's."[1] See the extensive citations at the link.
This is why I wrote "Public Education or something like it". We need education systems for literacy, however it does not to be compulsory or public if nearly everyone uses it and can afford it. It seems unlikely that these two conditions (affordable and widely used) would be met in our present society without public funding of education.
Note that in that article you link to they say that Southern Whites in the 1860s had a "56.4%" literacy rate.
So, effectively even at the subject you mention, literacy (english language communications), we are teaching less with 5 more years than we taught just over half a century ago (assuming that it hasn't improved since I left HS about 24 years ago).
I love technology... I love history.. and a lot of things.. that said, I think we're letting the core that is pure communication (reading, writing, and effectively communicating) is falling behind at the expense of being able to follow [INSERT_CELEBRITY] on [NEW_SOCIAL_MEDIA_PLATFORM].
Literacy rates have increased throughout the years: https://nces.ed.gov/naal/lit_history.asp
Without Public education or something similar to replace it is unlikely that we would have the high levels of literacy to which we are accustomed. Public Education successfully teaches most of the population to read and write English (including the children of immigrants whose parents may not speak English). This is a historically impressive feat.
1000 years ago the world literacy rate was less than 1%, 100 years ago the world literacy rate was less than 10%. Now it is roughly 80%!
It is clear Public Education could do much better, but lets not confuse failing to do better with failing to do anything or its most important job.