Schools Monitoring Students' Social Media

I read an interesting article about a school district in California hiring an outside firm to monitor the social media of students:

http://usergeneratededucation.wordpress.com/2013/07/23/steam-and-ma...

They are focused on finding instances of cyberbullying, threats of violence, or even mentions of suicide.  Opponents of the practice claim the students' privacy is being invaded.  However, the firm only looks at public posts that anyone could access.  They do not hack into accounts or view anything that the general public could not view. 

What do you think about this practice?  Do you think it's a good idea?