When to start formal essay

Hi,
I know I have been very active here lately! I am redefining our last 12 weeks of school and coming back to a more CM approach after a not so successful try at a more rigorous classical approach. In any case, I am wondering when most people start working on “formal essay” We are doing written narrations, about 2 per week and they are in 7th grade. I will up it to 3 times a week very soon. But I am wondering about starting more formal essays. What is the thought? I know that Charlotte didn’t start these until high school…..but I sometimes worry. I am not completely sure that I will be able to homeschool for high school due to health issues-that is in God’s hands right now. So I do want to make sure they are prepared IF they go. I am really hoping, and pretty much planning that we will homeschool for high school as we have homeschool the older two.

pam