Big 9-1 Blogging

I am experimenting this year with a blog in each of my classes. A student is assigned to each day and blogs a summary of what happened in class that day. I am using the blogging tool in Moodle. There have been some wonderful blogs by students who have practically written full lesson plans with example problems and encouragement to their peers. The main problem is getting the students to remember when it's their turn as they only blog every 28 days or so.