According to the report, published on Friday, the girl had been a pupil at Madras College in St Andrews while Mr Hiscox was training to be a teacher.
About two years later, she followed him on Instagram in October 2022 and their conversation turned to a sexual nature quickly, the panel heard.
The maths teacher exchanged sexual images and videos with the girl before agreeing to meet her at a hotel on 28 October 2022.
Evidence heard by the panel said the pair had drunk alcohol and had sex on a number of occasions during the stay.
Prior to the visit, Mr Hiscox asked her to bring her school uniform and offered to pay for a sex toy.
The pair had agreed to meet again, however the girl's parents reported the relationship to Police Scotland after she told them she was seeing her former teacher.
Because Mr Hiscox was not her current teacher and due to the pupil's age, no criminal offences were brought by the force.
However, the TRA found he was guilty of "unacceptable professional conduct and/or conduct that may bring the profession into disrepute".
In his report, Mr Oatley confirmed the teacher had accepted six of the eight allegations against him.
He contested asking the girl to bring her uniform to the meeting, stating that it was her idea, however the panel found the allegation to be valid.
Mr Hiscox also argued he did not know her age or that she was a former pupil.
But the panel believed the girl, who said she told him early on in their conversations and he replied saying "well it makes it even naughtier then".