Students are still working on their fish essays. As they move from graphic organizer to rough draft, I've found that it's very helpful to give them a rough draft template. I first created this back when I taught sixth grade. I was horrified to see that students were writing each paragraph on a separate sheet of paper! Somewhere along the line, they had started to see each part of the essay as a separate piece of writing.
The rough draft template helps students to see what their writing will look like in the end. I used text boxes to remind them of the job of each paragraph. This template also frees students to use some of my favorite writing tricks, like skipping the introduction at first. (I do so hate writing introductions!) They can easily see where the introduction should go, leave it blank, and jump right into Body Paragraph #1.
Like any scaffolding tool, I use this one just at the very beginning. By the end of the year, many students have enough of an understanding of structure that they can create essays without this support. I have gone back and forth on the merits of five paragraph essay. My current thinking is that if I teach it to students in fourth grade, then by middle school they'll be past its constraints and be ready to soar with new, more complex forms.
That's my hope, at least!