A teacher is facing disciplinary action at his school after he referred to a transgender pupil as a girl, although the student identifies as a boy.
Joshua Sutcliffe, a Christian pastor from Oxford, admitted he said "Well done girls" when addressing a group including the student.
He described it as a "slip of the tongue", but said he believed biological sex was defined at birth
The school said it would be "inappropriate" to comment.
Mr Sutcliffe, who teaches children aged between 11 and 18, said the incident took place on 2 November.
He said a week-long investigation found he had "misgendered" the pupil.
'Born a girl'
The maths teacher, who is also a pastor at the Christ Revelation church in Oxford, said he tried to balance his beliefs with the need to treat the pupil sensitively.
He claimed he did this by avoiding the use of gender-specific pronouns and by referring to the pupil by name.
"While the suggestion that gender is fluid conflicts sharply with my Christian beliefs... I have never looked to impose my convictions on others", he said
He said he had apologised to the student, but said he did not consider it "unreasonable" to call someone a girl "if they were born a girl".
More children seek help with gender identity
More than 2,000 young people, aged between three and 18, were referred to a specialist NHS clinic in 2016-17, seeking help with their gender identity.
The numbers have been growing every year since the start of the decade.
Of 2,016 young people referred to the Gender Identity Development Service (GIDS) in the most recent year, 1,400 were assigned female at birth.
Polly Carmichael, a consultant clinical psychologist and director of GIDS, said there was no single explanation for the increase but said there had been "significant progress towards the acceptance and recognition of transgender and gender diverse people in our society".
Dr Carmichael said the majority of the service's users did not take up physical treatment.
There were two children referred aged three in 2016-17. The service rejected 30 referrals of people who were already 18 years old.
The Christian Legal Centre, which is supporting Mr Sutcliffe, said he faced an internal disciplinary hearing on Wednesday.
The state academy school where he is employed said the matter was confidential.
However, it said it took equality and discrimination seriously and had a range of governor-approved policies in place to ensure it acted lawfully.
LGBT charity Stonewall said "pupils must be protected" even if teachers may hold "different opinions" about sexuality and gender identity.
It did not want to comment on the case involving Mr Sutcliffe, but it said "children should always feel included and accepted for who they are".