Sadly, some of the things I've heard about Kyron's home life lead me to think that he might have been more shy at home than he was at school.
I grew up with doting parents, so I was not shy at home.
I was comfortable with the kids at school and can't remember anyone at school calling me shy. However, my perception was that there were a lot of mean people in my extended family, with whom I had to spend a lot of time. When I had to be with them, I retreated into myself, and--not wanting to catch the dickens every time I turned around--I minded what I did and said pretty carefully. Thus, a lot of my relations described me as quiet, shy, bookish, backwards, or "such an awkward girl."
I think these days, in some blended families, there may well be cases where a child is more comfortable and relaxed at school amid friends than at home with a cranky or unsupportive step-parent ... or amid older, more domineering kids. I also think that a child might seem shy to a non-custodial parent, for a lot of different reasons. Not wanting to be too enthusiastic about the step-parent, for instance--or reasoning that there's no point in complaining to Mom about the way I'm treated, because she can't do anything about it anyway ... so I'll just clam up."
I'm not saying this was the case with Kyron in the months leading up to his disappearance--but I think it's at least possible.
MOO.