Activity in schools that attempts to persuade or convince, instead of safeguard and support, is essentially political in nature. Materials from lobbying or political organisations are expressly forbidden in schools, according to the Education Act 1996.
It is clear organisations like Mermaids and Stonewall are LGBT political lobbying groups and should have nothing to do with schools. Astonishingly, the Department for Education has recommended the use of Stonewall advice and materials.
Last month, however, the department issued new guidance, emphasising the legal obligation of schools to be politically impartial. Coalition for Marriage has published an excellent briefing paper on the guidance. Overall, the guidance is good news for those who hold traditional views on family, marriage and gender, where there is a real risk of schoolchildren with such views being made to feel there is something wrong with them.
If your school uses Mermaids materials, check out this article by Safe Schools Alliance with information and advice about getting them removed. if your school uses Stonewall resources, Christian Concern provides similar support for parents here.