YOU should first investigate the incident to establish whether the allegation was substantial and not a simple misunderstanding. If there is any chance at all that the student's work was wrongly influenced, the exam board must be notified immediately. An assurance should be sought that every effort will be made to ensure that the candidate's results will not be adversely affected, an assurance which will be important to the student and to the parents when they are advised of what has happened.
The exam board will expect the head, who is accountable to it for conducting the exam centre, to show that steps have been taken to ensure there is no recurrence of this incident. This may include debarring this teacher from acting as an amanuensis in the future.
The head will also wish to take disciplinary action and, in doing so, will need to establish whether this was an act of naivety, done in good faith, or a deliberate attempt to secure an improved exam result. In the latter case, the governors may consider dismissal for gross professional misconduct.