The teacher at the centre of an LGBT lessons row has received a death threat and other "nasty" messages that have left him feeling vulnerable.
Andrew Moffat, of Parkfield Community School in Birmingham, was told, "You won't last long", Sky News reported.
The assistant headteacher's No Outsiders programme has sparked protests, mainly by Muslim parents who object to their children learning about same-sex relationships.
Quick read: No parents' veto over RSE lessons, Hinds says
Background: Teacher shortlisted for global prize
Mr Moffat told Sky News: "I have had some very nasty messages and letters. I had a message to say, 'You won't last long.'
"So there have been some very difficult messages to receive."
Asked whether there had been death threats, he said: "I suppose you could say that is a death threat – you could look at it like that."
The news emerged as education secretary Damian Hinds said there should be no parent veto of what a school teaches in relationship and sex education.
Mr Hinds said he has been very concerned that teachers have felt intimidated by parents' protests.
Parkfield Community School has been the centre of protests following the introduction of the No Outsiders programme, which was developed by Mr Moffat.
The programme teaches according to the Equality Act, and Mr Moffat said you cannot pick and choose which parts of it to apply.
Pupils are taught about the positive values of diversity, tolerance and acceptance, in a broad curriculum encompassing LGBT rights, same-sex relationships, gender identity, race, religion and colour.
Last month, Mr Moffat revealed that the daily demonstrations outside the school gates had left some children in tears.
As a result of the disruption and negative effect on the youngsters, the school decided to suspend its No Outsiders programme until an agreement could be reached with concerned parents.
The PSHE teacher said the lessons do not make reference to sexual acts, and pupils are simply read stories where people have different families.
He said: "In Britain today, schools have got to find a way to tackle that rise in hate.
"We can't ignore this. We have got to find ways to teach children that if someone has got a headscarf on, I am not frightened of them.
"If someone has got brown skin and I have got white skin, I am not frightened of them. I can be friends with that person."