If I recall my K12 days, we had English grammar, English literature, Essay writing, and something else - can't remember. It was impossible to get into university without writing to a publishable standard. The reason was simple. If one cannot make oneself understood, how is a professor or reader able to understand what one is saying?

I think that one is either lucky enough to be exposed to peers or parents who speak well, or one is not. It's pretty much impossible to learn a language is one hears it poorly spoken.

For example, Americans always say things like "He did it bad' instead of "He did it badly.' That's because people speak that way.

The other factor is early reading. If one is not constantly reading throughout one's school years, it's unlikely one will pick up the rhythm of good writing. Most people don't read these days.

Also, good writers are essentially intellectuals - thinkers. They have above average intelligence. For some reason, nobody thinks of mentioning this fact.

Lastly, if one has to do a writing course in order to learn to write, then one cannot write.