Social Networking and Education

I wanted a while back to use Facebook in my classroom.  I had an idea to create a closed group (by invitation only) where students within my chemistry classes could interact to discuss homework, classwork, study questions, etc.  I had the idea that students (when off campus) could (when they saw something related to class) could upload pictures of what they saw for homework points.  (It is difficult to relate my class to everyday life.... usually.)  It (the idea) was shot down because big brother (Fairfax County Schools) was not in control.  I found this odd because my school's FCA, guidance department, and other organizations have Facebook groups.  Fairfax County Schools has a group for  parents and students to join.  Why it couldn't be used for chemistry is beyond me.  Concerns would be student confidentiality and student - teacher interaction.  An AP and IT monitor could balance the student - teacher interaction issue, and Facebook groups can be made private.  I don't see the problem.