I'm not sure what your definition of "disturbing things" means. If you could give us an example or two, that would be helpful.
However, if you believe that the students (or anyone for that matter) is endanger, you need to contact the school immediately. Give me specific examples of what your son says the teacher is doing or not doing. Keep a journal so you can record dates, times and a brief description of the incidents.
You can also talk with other parents who have children in your son's class to see if their children are making the same accusations. Don't turn it into a gossip episode, stick to the facts.
Volunteering in the classroom will allow you to see what's going on first hand. I do not suggest either you or your son caring a spy camera. I think that would get you into unnecessary trouble. Leave that up to the authorities.
You can buy backpacks that are all geared up just for these type situations. Though it may not be legal you can at least gain knowledge about what is going on in your child's classroom before you act. Here's a link to one but there may be others at various prices.
Teachers hurled insults like “bastard,” “damn dumb,” “’tard” and “a hippo in a ballerina suit.” A bus driver threatened to slap one child. A bus monitor told another, “Shut up, you little dog!” http://crackerpie.net/
I read a lot of stuff, and I found that the process of writing to clarify what I want to say it was very good, so I am impressed, and I would like to come again in the future. to be able to listen to higher quality again and administrators also have prepared a video clip of her as well.
give your kid a wire to wear to school, but before putting the illegal recording up on YouTube, embed your personal political agenda into the edited version with carefully crafted commentary that will be sure to touch a nerve in everyone