As stated above ranking can only refused to be given if by providing it it can identify other student's information.
Schools would be daft not to voluntarily give the CAG and rank that could be obtained by a SAR. Badly worded SARS could lead to schools havibg to provide all sorts of other information which could be quite onerous. Also if this takes too much time to get together it will be of no use for the purpose the student requires ie. to ascertain whether they feel there is a basis for appeal or to ascertain whether it is worth taking the exam. Ask informally just for those 2 items and I am sure they will say. If they won't just say you would rather not have to resort to a SAR.
Students will need to confirm that this information can be given to a parent if a parent requests it.