A teacher is being prosecuted for alleged sexual relations with a pupil at a school in Cornwall.
Police have also held criminal investigations into two other allegations which have not resulted in any charges.
Police confirmed the prosecution was taking place following a Freedom of Information request from the West Briton.
Neither the police nor Cornwall Council will release any information as to the identity of the teacher or the location of the school at which the alleged offence took place.
A previous Freedom of Information request to the council revealed ten teachers had been suspended following allegations of improper relationships at schools in Cornwall from April 2010 to March 2013.
All of those incidents were investigated by the police.
The West Briton then asked the police which of the ten incidents had resulted in a prosecution.
A spokesman for Devon and Cornwall Police said: “One offender has been taken to prosecution and the case is ongoing.
“For the other nine referrals to the police, two were investigated as criminal offences for which the police took no further action.”
The other seven cases reported to the police are understood to have not been taken further.