What does "extremely aggressive / violent" actually mean?
Physical assault? Shouting? Swearing?
If your daughter has made an allegation that a teacher, whether in class, or as part of an extra curricular activity has:
- Harmed a child
- Possibly committed a criminal offence against, or related to a child
- Behaved towards a child in a way that indicates they may pose a risk of harm to children
then there are set procedures that need to be followed and these are laid out in Keeping Children Safe in Education. The first of which is that the head teacher should have alerted the LADO (Local Authority Designated Officer) often called just Designated Officer.
The LADO (or DO) will take a view regarding whether the allegation requires any kind of multi agency response, or whether the investigation can be led by the employer.
To answer the rest of your questions:
If a child reports something like this should every school not have some kind of standard procedure for investigation & protection for the 'whistleblower'?
Yes, there should be a procedure that should be followed - even if an allegation is found to be false, or unsubstantiated, the school can seek advice regarding this from various sources. KCSIE has a good section on the outcome of investigations
How much information about that process and investigation should the parents be told? Is it public or private?
This is a tricky area - if it becomes part of a disciplinary process, then the teacher has a right to confidentiality. So, for example you could expect the school to give you general information, but they would not tell you that a teacher had been given a written warning.
Should any external organisation be involved?
Yes - if it meets (or possibly meets) one of the categories above. The LADO might also become involved if there were repeated lower level concerns. Other organisations such as the School Improvement Team (if the LA has one) could also possibly assist.
Is it appropriate for us to approach an external organisation if we are not satisfied with the outcome
Yes - referrals to the LADO can be made by anyone.
I have to say, despite your daughter being really keen to attend, I don't think I would be promoting it until I was convinced that the matter had been addressed appropriately, regardless of how disappointed she was.