First off, no matter how you do it, it's pretty much impossible to do a quality job of what this firm is promising for $2.89 per student per year. However, there are host of other problems here.

-A lot of bad jokes are going to create false positives, which will make teaching staff ignore the warnings they do receive.

-The odds are rather high that a kid will post an orgy of pre-meditations and then do something horrible, but this contractor will either miss it or his warning will be ignored.

-Kids don't like being spied on and will use social networks that aren't monitored. Some geeks might even try encryption or code-talk.

What would I do? Educate children about the importance of getting their friends help when they need it. The people who know kids best are their friends. Compared to this contractor, they won't fall for as many bad jokes nor ignore as many subtle danger signs. Teach children to be good citizens who care about each other rather than carefully tended and monitored potential threats.