Hi Julie,
I'm new to this forum and your post caught my eye. I recently started using SWI level C with 2 dd's, 11th and 8th grades and we've only worked through the beginning lessons. Both of my dd's have been doing written narrations for a number of years but we haven't begun any formal essay type writing. I do not consider this a whole credit/class but rather a part of a credit. I had an older son who attended high school and his 9th and 10th grade English classes devoted a 9 week quarter primarily to grammar and composition. The rest of the weeks were devoted to literature with writing assignments. My plan is to focus on this 3 days a week until we're finished. Like you, I like the structure and am hoping this will help my dd's to feel confident as they learn more formal writing.
HTH,
Linda