At the end of each week, my students complete a journal or blog entry, writing about their week at school, to their families. Students write about what we learned in each of the 4 subjects and the activities done in class. If time permits, they also write about PE/Options. I give them 45ish minutes on Fridays to write to their families. If their journal/blog is not finished, it becomes part of their weekend homework.
I have used both writing journals for this assignment and individual blogs (on kidblog) - both have worked well! I like this assignment because it opens communication between home and school - my parents love it too and write the nicest messages back to their kids. It also is an informal weekly writing assignment which helps develop basic writing skills (punctuation, paragraphs and writing with detail and description).
Enclosed is the digital parent letter that goes home at the beginning of the year to explain the assignment. Separate letters (one for a paper journal and one for a blog) are included in Word, for easy editing/customizing.