For our writing exercises, I try to always have my son write out a few sentences to describe what he is learning. For Bible, he write out verses or explains definitions of words. For Science, he writes a few sentences and draws a picture, etc. For reading, I have him write a few sentences about the chapter he read that day, and draw a picture, Pretty straightforward.
But I really want us to work on the discipline of writing as well. So I got a book that looked like it would be fun to work through, called Write Your Own Story Book. We are trying to work through the book in order of assignment, one per week. So far we have written stories about a detective in a strange museum, a parachuter who almost gets hurt (but not quite), a shy opera singer who wants a medal, and a letter to a boy in China, who has never been to America.
My son says he wants to be an author when he grows up, so I figure we should work on our writing 🙂