Practically speaking, the children should be writing across subjects, and in cursive.
We hope that are able to write at this age; if not, then we give them the tools they need to do so without belaboring the point. Just as with reading, short blips throughout the day are more efficacious than 20 minute or longer sessions at a time.
Provide experiences and studies so that the children *want* to write. Some children will not be enticed to write very much until they are more sure of their spelling and other abilities; that is ok. Just keep giving them what they need.
Other activities for the elementary child:
Filling in their work journals (they can draw pictures or diagrams, or write words, or use their imaginations to find another way to notate how they have spent their time that day).
Learn Calligraphy - usually 3rd or 4th grade
Study and learn illumination (link is to Wikipedia page).
Study other ancient forms of writing.
Study modern forms of writing.
Write samples of each for the enjoyment of it.
Focus on content and style. A curriculum is not needed, just a wide variety of experiences; but a guide to different styles of writing can be handy. Try something like Creative Communications, a collection of sequenced writing activities that build on a child's real daily life and interests. Please list other resources in comments so we can share these around!
Write letters, cards, thank you notes, postcards, definitions of words, instructions for games, new instructions for new or old games, how-to guides such as caring for plants or animals, grocery lists.... the list is endless to get children using writing in a practical manner. Then we can build into stories and essays and book reports.
The point is still interest and practicality - not drill and kill (as in, kill all interest for writing).