The teachers are absolutely right, and mold can harm their health and their students' health.
In fact, mold can lead to various diseases, and it is normal to avoid staying in a room infested with disgusting black toxic mold.
However, there was nothing to worry about as all they had to do was to find a mold inspection and removal service, like this one:
ssrestore.com.
I hired them myself, so I know for sure that they provide awesome service.
In case you still face the mold problem, check the site of the company I am talking about.