Help Needed with a Blog/Forum Assignment

Yesterday the other 8th grade physical science teacher approached me about doing some blogging with our students after the start of the new year.  Specifically her idea is to have a weekly assignment for students that would review science content from previous years as a way to prepare for the upcoming PSSA tests.  Biting my tongue so I don't launch into a diatribe about the ridiculousness of a standardized test on a non-standardized curriculum, I do believe this could be a great idea.  The question is how to pull it off considering it would be done with a total of 120 students.

I was reading the Tom Barrett's blog "Do You Have a Class or School Blog?" and found some great ideas but nothing to really aid me in figuring out how to pull this off.  I love the idea, presented in one of the comments, about having students taking turns blogging about the days class and then using their blog to start class the next day.  This might work really well with my environmental or biology classes in the high school, as well as with my 8th graders.  However, if we are going to do this with a PSSA focus, and such a large number of students blogging on a weekly basis, I think we need to come up with a different approach.

I am wondering if we would be better off doing this in Moodle using one of the various forum styles or setting up a blog page like Edublogs or Blogger.  I love the flexibility that Moodle offers for an assignment like this, but it lacks the more public appeal that the blogging sites have.  Maybe with the  specific questions students will be addressing, and the number of students that will be responding, the public aspect is not needed or even appropriate.  I would love for people to leave me some feedback in a comment to help me think through this assignment.  How would you approach this and what platform would you use to pull it off?  Maybe someone with a large following could retweet this to help increase the collaboration.  I am pretty new to this world and my PLN is fairly small right now... :)