Sure, but you’re basing this on the assumption that the parents will actually have the child’s wellbeing in mind. It begs the question of whether or not the parents will be abusive when they find out. LGBTQ+ kids have much higher rates of homelessness, because the chances of them being kicked out by (or forced to flee) their abusive parents is so high. The school (which is legally required to keep the child’s wellbeing in mind) has to take that possibility into account as part of the decision on whether or not to tell the parents.

If the child is coming out to the school but not the parents, it is probably because the child has already done that risk/reward calculation on their own and determined that the parents wouldn’t be okay with it. So that factor should weigh heavily on the school’s decision on whether or not to tell the parents, because you essentially have a kid saying “if you tell them, it will likely put me in danger.”