Well, the answer can be yes, but got alot of "but"s here and
there.
For me, you can blog about the teachers, as long as you post
with a certain amount of respect and understand what you should
post, and what you should not.
Students nowadays blog whatever they want, not caring about the
after effects of their post. They post racist remarks, slander
people and all sorts of stuffs. They should realise what
consequences they are facing, if anyone decided to press charges
against them.
Yes, you have your rights to do what you want. We're a
democratic society, but that goes the same for them. If what you
post did insult them, or tarnish their image with no proper base,
they can sue you. It's a fair system.