For my 14-year-old son, we used Intermediate Language Lessons (Serle) as a writing, poetry and grammar program for grades 4-6. It’s something you could jump into in grade 6 though, without having completed the first two sections, if I’m remembering correctly. We love that text and have two other boys midway through it right now; it’s small, non-consumable and we use our own composition books. In 7th grade, one son used a grammar text I wouldn’t recommend again; Analytical Grammar is likely a better choice. With my 2 5th graders we are using a few lessons a week from Rod and Staff book 4 in conjunction with ILL, and we skip the redundant lessons in ILL.
We’ve used and really enjoy Spelling Wisdom, and also take dictation passages from the boys’ history or literature readings. You could begin doing that a few days a week, as well as requiring a short written narration at the end of each week; perhaps I’d introduce one skill and wait a week or two before introducing the next.
A last thought; in transitioning one of my kids to written narrations, I sometimes took dictation from him and typed out his narration, at which point he’d copy it over in his composition book. We’d move from that to him giving it orally, and then writing it down once it was sorted out in his mind, to him finally being able to write it out on his own. I know we’ll be entering that phase again with my littlest soon…
