The TRA report said a local authority safeguarding officer raised concerns about Mr Bennington with the college.
According to the report, during an investigation by the college, Mr Bennington stated: "I was fishing really, to see if Former Pupil A was interested".
Mr Bennington resigned a week before a college disciplinary hearing.
According to the TRA report, Mr Bennington stated "he was embarrassed about what he had done" and admitted he should not have messaged the former student.
When asked by investigators if he thought it was appropriate to send a wink to a student, Mr Bennington said "no", according to the report.
He said he "unsent" some of the messages having realised he should not have sent them to a former student.
However, a TRA panel said it was concerned Mr Bennington "had not demonstrated any understanding of why the boundary between a professional and pupils is an important one".
In his judgement, David Oatley, on behalf of the education secretary, concluded that the conduct of Mr Bennington amounted to misconduct of a serious nature.
Mr Oatley said: "The lack of remorse and full insight means that there is some risk of the repetition of this behaviour and this puts at risk the future wellbeing of pupils."
Mr Bennington has a right of appeal to the High Court within 28 days of the decision.