That is a pretty huge use of the passive voice. There is nothing wrong with the passive voice, but it is used to dodge responsibility.
If it is the headmaster who will attach the note then the parents know who to sue/whose head to call for. If it is the school then at least they have an organization to protect their child from. The point of using the passive voice here is to try to make it seem like and untouchable authority will be behind it. It is a thing that will happen, there is no person or organization you can blame or fight against. More specifically, it is an attempt by the person writing it to avoid being blamed for something they clearly know they shouldn’t be doing.
I work for a government, and we do this all the time.
