I think the idea is that socialisation doesn't mean hanging out with your friends, it means any interacting with others. So queuing for lunch is included, as is anything other than silent individual work in class, etc. I think the most challenging and valuable aspect for my DS so far has been the simple fact of managing social situations without me being available to help.
That said, I'm horrified by the way US schools seem to have removed free play time. UK schools still have far more of it, I'm happy to say.
