Children will be allowed to learn about trans people who have undergone gender reassignment surgery but not “gender ideology”, the education secretary has said. Gillian Keegan said government guidance on sex education was aimed at stopping “gender ideology” that was “ignoring biological sex” being used in some schools. Under the guidance, which is being published on Thursday, schools in England will be banned from teaching sex education to children under nine. The guidance is expected to instruct schools not to teach children about “gender ideology”, and make clear it is a contested subject if asked. Keegan said this would not stop schools teaching children about people who undergo gender-reassignment surgery and that this distinction was a “sensitive way” to handle it. “Let me be clear on gender ideology in schools,” she told BBC Radio 4’s Today programme. “The thing that we’re trying to stop is not gender reassignment. Gender reassignment is something that is a protected characteristic – that adults are allowed to reassign their gender, there’s a process that they go through for that. That is a protected characteristic, and that can be taught. “Gender identity and ideology is something different, and this is part of probably similar campaign groups that have been building this set of materials and this ideology,” she said. Gender reassignment is one of the nine protected characteristics under the 2010 Equality Act, meaning it is against the law to discriminate against people on these grounds. Asked to give an example of inappropriate content being taught in schools, Keegan said: “I’ve seen some materials where they talk about gender identity being a spectrum, there being many different genders looking at, you know, trying to get children [to] do quizzes on, you know, what’s a different gender identity and what isn’t. Ignoring biological sex … a lot of that material has caused concern.” Keegan said she did not know how widespread the problem was, but that the government had taken action after some teachers raised concerns. “If I’ve got concerns and I think I can do something to help those concerns then my job, in my leadership role, is to address those,” Keegan said. “And that’s exactly what I do. I don’t shy away from it.” Jo Morgan, a former teacher and the chief executive of Engendering Change, which runs sex education workshops in schools, said ministers had not made clear what they meant by “gender identity” teaching. “Presumably they are concerned that teachers are teaching students that sex and gender are different things, and therefore that you can change your gender,” Morgan said. “And they are concerned that schools are becoming breeding grounds for transgenderism. There’s no evidence to support that. “What we are doing as educators is saying, this is in the news, in social media, it’s everywhere – let’s unpack it together and look at what sources of information you are being exposed to, let’s talk about how this relates to the Equality Act.” Morgan said that not teaching such a contested and prevalent topic would be “doing children a disservice”, adding: “If I was doing a lesson on gender and sexuality, I’d be saying: ‘Some people have this view, others have this view, what do you think?’ Teachers are not standing there saying: ‘You’re all transgender.’” In an interview with the Telegraph last month, Keegan said she would stop using the phrase “trans women are women” and that her understanding of the issue had “evolved”. On Thursday the education secretary told the BBC that when she used the phrase in the past, she had been referring to people who had undergone surgery. “I’ve always known that trans women aren’t women,” she said. “Somebody who has changed their gender, who has changed from a man to a woman, who has gone through the full reassignment, was who I had in my head at the time. “Somebody who was a man, that has transitioned, that has fully transitioned, is known as a woman. “There’s a huge difference between self-identification, people who want to identify but still have a male body – biologically are male, and then there is a very, very small number of people and I think we have to be really sensitive … who have had gender-reassignment surgery. “I personally believe that if you’ve gone to that level … then you are legally and medically allowed to say you’re a woman,” she said.