While i think that we often tend to over-emphasize decline, and that we too often point back to a mythical golden past when things were allegedly better, it does seem to me that things have deteriorated in some particular ways over the past couple of decades.
I teach history at a state university here in California. Our students are taken from the top third of the graduating high school classes of the state. And yet, even in their sophomore and junior and senior years, many of them still have no idea how to write. I’m not talking about stuff like split infinitives or other pointless rules like that; i’m talking about things like subject/verb agreement, inability to use apostrophes, incorrect usage, and, in come cases, sentences that simply don’t make sense no matter how hard i try to decipher them.
Unlike a couple of other people in this thread, i’m not sure that the culprit here is a lack of formal grammar instruction in the schools. I had very little formal grammar during my school years, and yet i still graduated with an ability to write coherent sentences. In many cases, i think that the reason for shitty writing ability can be blamed on the fact that many students simply don’t read very much. I know they read text messages and emails all the time, but it’s clear to me that many of my students don’t read anything in the way of proper, grammatically correct writing. They don’t read books, magazines, newspapers.
While i didn’t get a lot of formal grammar instruction, all the reading that i did allowed me to learn, by a process of absorption, what a good sentence looks like. And i’m not saying that the reading needs to be highbrow literature. I didn’t spend my childhood and teenage years reading Joyce and Austen and Melville; i read cheap adventure stories, science fiction, spy novels, and stuff like that.
As i said, i teach university history, and one of the most common complaints that i get on my student evaluations is that i require too much reading. In my upper division history course, i ask my students to read about 50-70 pages a week. And that is far less than i would require if i were teaching at a top-level college. When i worked as a TA during my grad degree, at Johns Hopkins, it wasn’t unusual for upper-level history courses to require well over 100 pages a week. But my student evaluations are constantly full of complaints about how much reading they have to do, and it’s clear in class that only a small percentage of students do all of the required reading each week.
If someone doesn’t read, and has had little or no formal grammar instruction, it shouldn’t be very surprising if that person is not a good writer.