Students often think "well-written" means grammatically correct.
There's certainly a correlation between good and correct, but the two are not the same thing. Some great bits of writing (including some of my favorite books, and several texts assigned by the writing program that currently employs me) are filled with grammar errors. They're still good.
Meanwhile, sometimes even sentences or headlines that are grammatically correct are badly written.
Take, for example, this recent headline from the Press-Enterprise: "Mojave Desert: Tortoise finds curtail solar-site construction."
The headline is perfectly correct. Heck, it even contains a complete sentence, which is odd for a headline. That's the first rule that usually goes out the window.
But my bet is most readers couldn't make sense of it, or tried reading it but gave up after deciding it was grammatically incorrect. When I first read it, I was thrown off by the word finds, and ended up shaking my head in confusion. I had to look at it twice to figure out what was intended by the headline writer. (The headline writer is probably not the journalist who wrote the article -- those are usually different people.)
Finds in the headline is a noun, not a verb. It's being used in the same sense as "Wow! What a find!" It's a noun meaning something that's been found. They found some stuff related to tortoises. Usually, when we see find used this way, it's a singular noun and it's modified by a clear adjective, like archeological. If the headline had said, instead, "Archeological find curtails solar-site construction," those of us comfortable with the word curtail probably would have understood it just fine.
The problem is that we can imagine a tortoise finding something, and finds with an "s" at the end is less familiar. Moreover, finds agrees with tortoise, so just about anyone reading "tortoise finds" is going to picture a tortoise saying "Aha!"
Readers who don't know the word curtail will picture some sort of vague thing that can be found: "Ah, the tortoise found a curtail, whatever that is." But then the rest of the sentence makes no sense. For those of us who know all the words, we're lost as soon as we hit curtail -- two verbs in a row? That's peculiar. (Then again, I did just read a student paper in which a sentence said "Recently, a judge wrote admitted ..." In that case, it was an error.)
It's tough to avoid these. Pretty much everyone creates a sentence like that at some point. However, most of the time, if you take the writing process seriously, you can catch this sort of thing. Peer reviewers can circle the sentence and write "huh?" in the margins, prompting you to look at the sentence again more carefully. Reading it aloud (or having a buddy read it to you) can help you catch stuff that's easy to mis-read. My point isn't that the Press-Enterprise screwed up; the paper has tight deadlines and these writers are often more rushed than students are. (Hard to believe, but true.)
My point, instead, is that students who want to dramatically improve their writing should review their work not just for errors but for wording that simply doesn't work, regardless of how grammatical it is.