I would recommend Excellence in Writing (EIW) for grammar and composition for a new homeschooler. Very straightforward and the parent or guardian doesn’t have to do the teaching. It takes the child step-by-step through everything. It’s not overwhelming and in my opinion it’s age appropriate for each level. I looked into IEW for composition, but it seems way too overwhelming. However, I do think the daily sentence editing of Fix It! Grammar is a good option for grammar.
