I just want to point this out, the original scenario that Libby was getting so worked up about, doesn't represent any kind of child endangerment.
Gloria comes to school and tells the class teacher: "In class, would you use he/him pronouns for me and use Dennis? I've tried telling my parents I want to be Dennis, but they don't listen to me: I'd like to be Dennis some of the time." (I'm summarising this for the sake of space - I don't really expect a child would put it that compactly.)
Teacher (obviously) discusses this with their headteacher and other appropriate people at the school. The school concludes that if Dennis is happier when called Dennis in class and the teacher uses he/him pronouns, no harm is being done and there is no obvious reason to tell the parents instantly.
Several things might happen, including, quite possibly, Gloria coming into the classroom after weeks or months of being Dennis, and saying "Changed my mind, I don't want to be Dennis, call me Gloria and use she/her".
Or Dennis telling the teacher "I want to be Dennis all the time now" and the teacher pointing out that this does mean sitting down and talking to his parents. If Dennis doesn't want to take that step but is happier being called Dennis in class, again - how is this any indication that Dennis is in danger? The longer Dennis goes on being Dennis at school, the more strongly the school are, justly, to feel that there needs to be a conversation with the parents - not least because (as a post well upthread made clear) it's unreasonable to expect the other kids in class to not say that Dennis is Dennis.
But the notion that the majority of commenters on this thread seem to have, that it would be wrong to allow Dennis the freedom and space to find out for himself that he wants to be Dennis all of the time (and, conversely, the freedom and space to find out that Gloria didn't want to be Dennis any more, having tried out beng Dennis in real life) because the parents have got to be told instantly, because their minor child has zero right to decide for themselves when to have that conversation with their parents about being Dennis. It is not "safeguarding" - and indeed, Department of Education guidelines make this clear - for a child to know they have no adults they can trust in their life.