Jeffrey Tansey, 40, was a teacher at Aylesbury Grammar School when he contacted the girl on a dating website.
A National College for Teaching and Leadership panel heard he first thought she was 18 or older but then met her despite knowing her true age.
Mr Tansey denied his behaviour in 2012 was of a "sexual nature".
During the conduct hearing, Mr Tansey said he only met up with the girl - who was not a pupil at his school - "in order to assess her vulnerability, offer her support" and to help prevent "her from putting herself at risk in the future".
However, the panel said it did not find his explanation "credible", adding he had referred to the meeting as a "date", held hands with her and twice exchanged "closed mouth kisses on the lips".
In finding Mr Tansey guilty of acting in a way that might bring the profession into disrepute and showed a "serious lack of judgement", the panel banned him from teaching in England.
Aylesbury Grammar said in a statement: "The school acted promptly in suspending the teacher pending both a police and internal investigation.
"He was subsequently dismissed from his teaching role at the school in November 2012."

Plymouth-born centre-back Ellis, 28, has made just 12 appearances since joining the Cumbrians from Shrewsbury on a permanent basis last summer.
It is his second spell at the New Lawn, having spent the 2009-10 season with Rovers on loan from Torquay United.
The deal follows fellow defender Charlie Clough's move to Barnet for an undisclosed fee on Monday.
A grammar school teacher has been banned from working in schools after he went out with a 15-year-old girl he met on a dating website.
[NEXT_CONCEPT]
Carlisle United have loaned defender Mark Ellis to Forest Green Rovers for the remainder of the season.