I use the Writing Curriculum from Teacher’s College at Columbia. The curriculum focuses on teaching kids to progress through the stages of the writing process, from planning and subject selection, to drafting, revising and editing. The year is broken into units, so that kids at each grade level learn to focus for a number of weeks on understanding different types of writing. Persuasive opinion pieces, nonfiction informational writing, personal narrative, etc.
The program is very self-explanatory, with specific suggestions to tailor the lesson to the child’s progress. Each topic in the curriculum is detailed in a series of lessons that pace out over a few weeks. I love that the program uses books as examples of good writing! You read together to notice specific techniques the author uses. Ultimately, this program is about developing various writing strategies to bring to the table, no matter the topic or the task. Writing is designed to be a daily, beloved task. When I get my daughter to actually sit down for her writing, she always ends up really liking it.