This from Mermaids current website:
“Supporting a transgender child as a teacher
You may encounter children or young people who are struggling with their gender identity and this can be difficult and confusing at first. That’s perfectly understandable and it’s great that you’ve come to find out more.
Under the equality act 2010 any young person has a right to be addressed as their true gender, regardless of any diagnosis or medical intervention and irrespective of age. We have a number of resources that identify the responsibility you have as a school towards these pupils and your duty of care.
Mermaids and other partner organisations can assist your school to assist with a child or young person’s transition, provide training and lesson plans to make sure the best outcome is achieved for all involved. The most important thing is that the young person is respected and their views listened to”
So yes, they do provide lesson plans, and might do well (as might Stonewall) to check that the requirement to be evidence based doesn’t fall over on misrepresenting the Equality Act, as they both have definitely been doing to “get ahead of the law” (which now won’t be changing in the direction they anticipated).