How much privacy

does a teenager have - say someone up to the age of sixteen? That "sixteen" is not an arbitrary figure because it is the age here when a "child" can leave home and become independent.
Someone posted a message on Facebook yesterday about their daughter - not yet sixteen. The girl had made an appointment to see a nurse without informing her mother. She needed a note to go - which she had obtained from the medical centre - but had confused the day and the school would not let her leave. Instead they phoned her mother to check - thus letting her mother know about the appointment for the first time.
Now of course the first thoughts of many people, perhaps even most, would be that the girl is seeking contraception advice or help - or perhaps that it is a drugs issue.
In this particular instance the girl, like other members of her family, has a genetic disorder and trips to the medical centre are a frequent occurrence. Her mother had been away and the girl had been mature enough to (a) recognise the need to seek advice and (b) do something about it.
The problem was a rather different one. Teens are supposed to be able to seek advice without the consent or knowledge of a parent.
It is a legal minefield. I am glad I am not working in schools anymore or in the medical profession. I am glad I am not the parent of a teenager.
But I do sometimes have responsibility for the Whirlwind. She happened to have a dental appointment. As she boards at school the school got her there and I met her afterwards. On the way back to school I asked her what she thought of the situation. 
Her response was the sort of response I thought I would get.  What it amounted to was that there should be communication on the issue. If the parent knows there has been an appointment made then it should be mentioned. The parent should say, "I know because the school phoned me" and "do you want to talk about it?".
I have been thinking about it since then. It's a very awkward issue. It is not just an issue of "trust" or "confidentiality". There are also issues about maturity and decision making. I do not doubt that there are some younger teens who are capable of making very mature decisions but there are others, especially faced with a crisis, who are not. And should teens who are not of a legal age to consent be able to go to medical staff and ask for contraceptive measures - and ask without the knowledge of their parents?
It is not likely to be an issue for the Whirlwind. She boards at a single sex school and their movements are tightly controlled. At weekends her father keeps a close watch. So far she has shown no interest in boys as anything more than friends - with the occasional comment to me that someone "looks pretty cool". She also knows that school rules say and her father and I agree that she won't go out alone with a boy until she is sixteen. Even then there will be some rules. It is not, as the school and her father have emphasised, that the girls are not trusted but because they are trusted - trusted to have the maturity to understand the potential dangers in relationships.  Is it invading the privacy of the girls? How much right to privacy do you have when you are still legally a child or young person and you are still financially dependent?
They are interesting questions for me - and probably for my siblings. My mother believed we had no right to privacy at all - even as adults. We were expected to show and tell her everything. The result of course was that we tried desperately hard to keep secret even things that did not matter in the least.
When I was teaching I can remember asking a boy who had a reputation as a troublemaker why he had always behaved for me. He looked at me and said, "Well you said you trusted me to do the right thing."
Is that what it takes? Do we need to tell teens that we trust them to do the right thing - and then perhaps make them believe that trust is important?