The Christian Institute is urging schools to cut ties with groups that promote radical ideas around gender identity.
It follows the introduction of new government guidance on the Relationships and Sex Education (RSE) curriculum telling schools that they "should not reinforce harmful stereotypes, for instance by suggesting that children might be a different gender based on their personality and interests or the clothes they prefer to wear".
The guidance adds that schools should not work with external organisations that create resources promoting such ideas.
"Resources used in teaching about this topic must always be age-appropriate and evidence based," the guidance reads.
"Materials which suggest that non-conformity to gender stereotypes should be seen as synonymous with having a different gender identity should not be used and you should not work with external agencies or organisations that produce such material."
Welcoming the guidance, Christian Institute Deputy Director Ciarán Kelly said schools had "for too long" been "harangued" by LGBT lobby groups "to promote and adopt a mindset that pushes harmful gender stereotypes on unsuspecting children".
"Radical trans ideology is being expelled from the classroom – and not before time," he said.
Mr Kelly said the guidance from the Department for Education made it "clear that all such ties should now be cut, any associated materials consigned to the recycling bin and that parents have been given the green light to hold schools to account on this".
He said this should include story books that encourage children to think they have been 'born in the wrong body'.
"But there's a wider point too," he continued.
"The guidance now explicitly acknowledges that teachers and pupils alike should be encouraged to hold and express a variety of views, and they should not have a particular position pressed upon them."
Earlier this year, Warwickshire County Council was forced to withdraw a controversial primary-age RSE programme that included graphic sexual images and covered self-stimulation while ignoring marriage, despite not being classed as a sex education resource.
The programme erroneously taught that gender identity "can be best understood as being a spectrum" and "transgender children have the right to use whichever toilet or changing room they feel most comfortable using".
The programme was pulled after The Christian Institute threatened legal action.
