This will be interesting.
I'm actually shocked that teachers ever thought it a good idea to keep such a big secret from parents.
Having had the pleasure of a long walk home with my head of year next to me to inform my mother of something I'd said as school, (I begged her, cried, etc, not to have to tell my mum. She even gave me a week to tell her myself). But no matter how much I protested safeguarding meant the teacher had to tell my mother.
And that was despite knowing my mother was not going to be happy and I was likely to suffer fallout from it at home.
Teachers should not keep secrets from pupils parents.