The elephant in the room is that such programmes not only need to be operated privately in order to encourage kids to get tested & treated - for some kids if their parents know about this, particularly if they have chosen to be tested, it could actually be dangerous for them.
I still remember a girl at school with an unplanned pregnancy who asked the school to help her tell her parents - she had good reason to do this and actually it was deemed necessary for her safety for her to be removed from her family home, basically cos her dad lost his shit!
So PLEASE discourage your son from telling you or ANYONE else which other kids have been tested, and IF he does anyway DON'T go telling anyone yourself!
"In Scotland over the age of 12 the doctor does not let u in room with ur child unless child says I want u there so I don't think they need ur permission as they of legal age to go to docs on own" I don't think there's an official age, but yes they're encouraged to manage their own appointments once they're high school age and are asked if they want parent in there if they might need to ask eg a girl with stomach pains if she might be pregnant.
I always said to dd I'm happy to leave if she asks but she was happy to have me in with her until she was about 15/16 at which point it was daft me even going with her unless she asked me too (I'm a bit more confident bolshy so if it was something she was banging head against brick wall with Drs about she'd ask me to go with her), as she was able to deal with most things herself.
She manages her sexual health well I think, still talks honestly with me about it, even though I don't specifically ask. She knows I'm here to discuss any time she needs to. But if she didn't I'm confident she's sensible & responsible and has been for a few years now (she's 18 now).