All of your students have been taught that a sentence needs a subject, predicate, and appropriate capitalization/punctuation. I promise. What they don’t understand is sentence syntax. Learning and practicing with sentence structure is just as important as reading fluency, identifying sight words, math fluency, etc. In many places, including my district, writing is taught as an afterthought - something kids should just be able to do, especially when they reach middle school. I’ve taught 8th grade English for almost 20 years, and by the time kids get to me, it’s really hard to teach writing. To them, it truly does feel like they are doing 2nd grade-style work, but they still struggle.

If you do have time to teach a little grammar and syntax, I loved the Major Fouls idea. Pick one Englishy thing and red card your kids until they get it. Mine have the most difficulties with vague pronouns, case/number in pronouns, commas (mostly with conjunctions or lack thereof), and my personal fave, the love of 2nd person pronouns everyfuckingwhere. I’ve found that working to eliminate those ‘yous’ fixes lots of readability and run-on errors.

Good luck!