If you haven't already, read through the example post, then read this.
Again, note that you need not go to the hassle of creating an anonymous blog if you don't have "inappropriate" things to say.
Note the fact that a name is never mentioned; neither of the publisher nor of his teacher/principal. While the latter is probably overkill, if you have a small class and you do not rotate classes throughout the day it's probably not a good idea to mention your teacher's name in your rant.
Also, if they do something to you in class that you want to rant about, write it from either the third person or from an anonymous bystander's point of view. If she gives you a bogus detention and you say "she gave me a bogus detention," it's gonna be traced right back to you.
Overall, it should be fairly simple to see how this poster's blog would be untracable if he kept to the basic rules of anonymity. If you have any questions, please email us.