Kelly - a homeschool mother of five on the West Coast, wrote this:

I would recommend Time4Writing as a good supplement for any homeschool curriculum (including SOS, which we used briefly years ago).

Even if the curriculum you are using includes writing practice, it will lack the personal teacher feedback of Time4Writing. I can't tell you how valuable that feedback was to my children! Often, the teacher would mention something I had "nagged" my child about for years . . . but it was a little more credible, because someone ELSE thought the same thing.

For me, this clarified in my mind who much  impact Time4Writing can have on a student's writing skills.