In writing a reference, the writer has a legal duty to the subject of the reference to be accurate and fair. A similar duty is owed to the recipient of the reference, with the additional duty of responding to any specific enquiries.

You wrote a reference in good faith, based on the information available to you at the time. Clearly, you would have referred to the disciplinary action had the matter been known to you at the time, and you now feel that the new employer is entitled to know about it. If the offence had been one of gross professional misconduct, which would have led to dismissal, the new school might have wished to consider this teacher’s position. As it was not, they would be in no position to do anything, unless they could demonstrate that the teacher had deliberately withheld information which was asked for on the application form or at interview.

There can be no objection, therefore, to your acquainting the new employer with the facts, although it would be courteous to notify the teacher in advance of your intention to do so. This would give him the opportunity of volunteering the information himself.