A disciplinary investigation learned how Matthew Sides, who taught in Hartlepool, thought the child was 16 before he “called the police and made a voluntary confession” after discovering the boy was just 14.
Sides was arrested, placed on immediate leave of absence from work and eventually suspended as inquiries continued.
While “the police decided to take no further action”, he was sacked by Eldon Grove Academy before the Teaching Regulation Agency (TRA) launched a misconduct investigation.
A 17-page official summary of its findings tells how Sides, now aged 28, contacted the boy – identified as Child A in the report – on social media via the Grindr dating app before twice engaging in sexual activity with him on separate dates.
Both Eldon Grove and the TRA stress that the incidents took place outside of school and did not involve one of its pupils.
The report says: “The panel was satisfied, on the balance of probabilities, that Mr Sides had believed Child A had been 16 when he had engaged in sexual activity with Child A.
"However, the panel considered that Mr Sides had completely neglected his duty, as the adult and as a teacher, to take steps to ensure that Child A was in fact 16.”
It also notes: “Child A told the police during their investigations that the encounters and sexual activity were consensual and without pressure.”
Finding three misconduct allegations against him proven, the panel “was satisfied that the conduct of Mr Sides fell significantly short of the standards expected of the profession”.
The report adds: “The panel determined that Mr Sides’ awareness of the risks to Child A, himself, the school and the teaching profession had been woefully inadequate.”
The panel recommended that he could ask for his ban to be reviewed after five years as it “did not consider that Mr Sides had used his teaching position to influence or exploit a person or persons”.
It also heard from the anonymised author of one character reference how Sides previously “had an impeccable record”.
A second reference stated: “Matthew’s prohibition would be hugely detrimental to the teaching profession.
"He has successfully worked with children around the world, but his biggest impact has been on the young people of EGA. His loss has been felt throughout the school.”
But decision maker Sarah Buxcey, who reviews recommendations for the Department for Education, felt the panel gave “disproportionate weight to the mitigating circumstances in this case”.
She added: “The fact that Mr Sides proceeded to engage in sexual relations with Child A, someone he met briefly on a social media platform, without taking responsibility to check the correct age, posed a risk to the child, himself, the school and the profession.
“I consider therefore that allowing for no review period is necessary to maintain public confidence and is proportionate and in the public interest.”
While Sides cannot ask the TRA to reduce the terms of his indefinite ban, he has until August 28 to launch a High Court legal challenge.