Generally ammonia will destroy this kind of
mold. I know people recommend other liquids, but
ammonia is the way to go. Before using the ammonia the room should be "dewatered" with use of one of more dehumidifiers. These molds like moist places. In the case of a school, professional help is advised, but in a bathroom use a spray bottle with 100% ammonia, go in, hold your breath and spray a three foot by three foot area. You should practice this.