By the time you get to collecting your A Level results, almost all students apart from the very, very youngest in the year will be 18. It's absolutely ridiculous that you should have to have your parents with you when you're a fully grown adult. I found it incredibly odd having a parents evening in Y13. I was an adult! It just didn't feel right at all.
Also, I like to be able to get my results on my own and process them in my own head before telling anyone else. My parents would probably jump for joy no matter what results I opened (even if I failed everything, they would be like "oh it's not that bad, well done, we're so proud") and I guess that's a really good thing - but not what you need when you're overcome with disappointment.