Parents should not be told if their child comes out as trans, the Chief Rabbi has advised schools.
Guidance says that "any information about staff or pupil sexuality or gender identity should be treated as confidential" and not disclosed to anyone "including their parents".
It warns that making the parents aware if a child is trans "can itself be a safeguarding risk" as teachers do not know how they will react.
A spokesman for the Chief Rabbi's Office said that the advice related only to disclosures about gender identity and not moves such as a change of name or pronouns.
Campaigners claimed that the guidance runs contrary to basic safeguarding principles and said that they were "shocked by this attack on families" by the religious leader.
The Prime Minister has previously said that he is "very concerned" teachers are not contacting families when a child questions their gender.
Rishi Sunak said that he has been "clear that parents must be able to know" what is going on in schools.
The Department for Education (DfE) will publish instructions on dealing with gender issues before the end of the current school term.
The long-awaited government rules are expected to say that families must be informed if a child asks to change their names or uniform.
A spokesman for the Chief Rabbi's Office said it will review the guidelines once the DfE publishes its document.
It is not advocating "withholding important information about students' lives from parents" who are "unquestionably the primary guardians of their children's welfare", he added.
The Wellbeing of LGBT+ Pupils: A Guide for Orthodox Jewish Schools was produced alongside Jewish LGBT charity KeshetUK and first released in 2018.
In a section marked "safeguarding and confidentiality", it said that "all staff should be clear that a pupil coming out is not a safeguarding issue".
It added: "Like any other personal information, any information about staff or pupil sexuality or gender identity should be treated as confidential. Unless there is a risk of harm, this should not be disclosed to anyone, including their parents.
"Making a pupil's parents aware of their child's sexuality and gender identity can itself be a safeguarding risk, particularly as the school cannot know how parents or carers might react."
If a pupil says that they are at risk of harm because of other people's reaction then the safeguarding lead should be informed, it said.
It also discussed training all staff to prepare for a child "coming out" to them, adding that they should not disclose it to anyone, "especially their family or teachers who they may not wish to tell".
A report by the Policy Exchange found that schools were routinely not informing parents when a child was questioning their gender.
The report concluded: "The law and the safeguarding principles based upon it is very clear: 'unless the contrary is shown' parents should always be involved with regard to a child's welfare."
Tanya Carter, of Safe Schools Alliance, said that Chief Rabbi's advice runs counter to basic safeguarding principles.
"One again we are stunned at the poor understanding of safeguarding from people who should know better. It is the basis of safeguarding that all adults in a child's life need to be working together for the benefit of that child," she said.
"The only exception to the rule of speaking to the parents would be if you felt that speaking to the parents would place the child in danger, in which case you need to follow your safeguarding procedures.
"We are really shocked by this attack on families by the Chief Rabbi."
A spokesman for the Chief Rabbi's Office said: "It is certainly not the case that our guidance advocates withholding important information about students' lives from parents. Parents are unquestionably the primary guardians of their children's welfare and it would be irresponsible for a school to regard them as anything else, unless there are specific safeguarding concerns.
"It is the case that where a child confides in a teacher about their sexuality or gender identity, it could be harmful for that teacher to share details with a parent before the child is ready to do so. Teachers must of course communicate with parents but think carefully about how and when this is done.
"When we review this particular document following the imminent publication of the DfE's own guidance on the matter, we will look at whether we need to make the section on this point clearer."
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