NewsActivist (http://newsactivist.com) was created in 2012 by teacher Gabriel Flacks, Humanities Department Coordinator at Champlain College Saint-Lambert. This free site is being used by students who are collaborating across classrooms and across the world. You'll find students writing about a broad array of topics, typically as part of specific assignments in college classes.
We've used NewsActivist at The College of Westchester and students and teachers alike have found it to be a productive, engaging experience.
If this sounds like something your students might benefit from, click over to their About Page, here: http://newsactivist.com/en/global-educational-network-designed-and-teachers-and-students, and think about registering your class!