A legal "loophole" is preventing parents from finding out what their children are being taught in school sex education lessons, peers in the House of Lords have warned.
The peers were speaking in support of an amendment to the Schools Bill tabled by Baroness Morris of Yardley seeking to increase transparency around material provided by external organisations.
Baroness Morris of Yardley said there was a "very big loophole" affecting parents' "visibility" of what is being taught to their children in relationships and sex education (RSE) lessons.
She said she had been contacted by a mother who was told by her child's primary school headteacher that she could not see some of the material being used in the RSE lessons "because the organisation that was delivering that part of the curriculum said that it was exempt under Section 43(2) and Section 42 of the Freedom of Information Act".
"The law allows it to claim that parents are a third party. That cannot be right," she said.
"It does not matter whether they like the curriculum material or not. This particular bit of curriculum material was, I think, very contestable in terms of appropriateness for age.
"However, even if I thought it the best bit of teacher material I had ever seen, I would say it could not be right that a parent could not have access to it and see it.
"There are so many areas where a parent would want to know what is being taught to a child, and something needs to be done about this."
She added that the loophole was putting headteachers in the difficult position of having to come between parents and external providers, potentially damaging their own relationship with parents.
"Whether we like it or not, we live at a time when there are lots of curriculum areas in which facts are not facts, and what we all assumed was appropriate to pass on to the next generation is now being contested," she continued.
"We have contested information and different views; as a society and a generation we are trying to work these things out.
"It is critical that giving ideas and words to the next generation is done with care, openness and the support of all the adults possible."
Lord Knight of Weymouth, supporting the amendment, agreed that parents should not be treated as a third party.
"They are an integral part of the community, and for community cohesion purposes among other things, it is important that such transparency exists," he said.
Baroness Fox of Buckley said that the reliance on ready-made materials from outside providers was "actually undermining the professionalism of teachers" and had created "a situation where there are all sorts of people going into schools and teaching things and nobody knows what they are teaching".
"These experts can be used to train governors and teachers or to run workshops directly with pupils and to supply materials, as we have heard," she said.
"But when you look at who is doing it, some of them at least are partisan political activists who embrace one-sided ideological approaches to contentious issues.
"They are not trained as teacher trainers, they are not accredited and there is no central regulation."
Instead of taking control of the situation, she said the Department for Education "seems to be washing its hands, saying that it is up to schools to vet third-party providers".
"But without clear guidelines it is hard for schools to navigate around what are, if we are honest, contentious culture war issues," she said.
She added that some of the resources were teaching "more ideology than facts".
"I think the excuse is that the material is commercially sensitive, but often what is going on here is that things are politically sensitive. These are not benign ideas, let alone facts; they are often divisive and totally at odds with parents' values, and certainly fall short of statutory requirements for teacher impartiality," she said.
Lord Macdonald of River Glaven referred to the government's guidance on RSE which states that content should be age-appropriate and anchored in science and facts.
Contrary to this, he said that some schools were using "ideologically driven materials not grounded in science".
"It seems that a significant number of independent so-called RSE providers have created materials that promote to schoolchildren, including quite young children, the idea that biological sex is a spectrum, that we all have an inner gender identity that should take priority over biological sex and that our assumed genders are assigned to us at birth," he said.
"One may agree or disagree with those propositions, and one may agree or disagree with them being put forward as scientifically based fact, but it is also clear that the 2019 guidance made paramount that parents should have visibility of what is being taught to their children."
He added: "There is clear evidence that the 2019 RSE guidance has resulted in some schools using ideologically driven materials not grounded in science, in my view, with children, including some very young children.
"This has particularly been so in the field of gender ideology, where some materials appear to deny the reality of biological sex. These teachings have consequences, not least for women's sex-based rights."
He added that, in spite of government guidance, it "has become apparent that some external resource providers, including some with a notoriously fixed and driven view of these matters, are actively seeking to prevent parents seeing the materials being used, including by using arguments based on commercial confidentiality".