And for all my pre-worry and stressing, it went very well. We (Thing Two, the friend, and I) bowled two games at the bowling alley, then I gave them some quarters for the video game machines before taking them back to our house. After a snack, they settled in with the Wii since the thunder outside had taken swimming out of the equation, and were still playing together in peace and harmony when the friend's mom arrived to pick him up.
We've made some good progress since the early, ugly days of the first playdate attempts. There was no crying at transition points (time to leave the bowling alley, etc) today. No inappropriate hugging. No really silly behavior or voices or unnecessary loudness. To the extent that his bowling alley etiquette was a bit off, it was indistinguishable from that of his NT friend (and not that bad), so I let it go. He remembered to ask his friend what he wanted to play at our house, and he said "thank you for coming" at the end with minimal prompting. Sounds like small potatoes, sure, unless you have a child who struggles socially, at which point any one of these things can pose a major challenge. For us, these are not things we've been able to take for granted.
The biggest problem we had today was me, which hurts to admit but is the truth. I need to back off and just let them be, not hover so much trying to make things go well. This friend in particular has been in Thing Two's class for two years now and seems to like him, idiosyncrasies and all...not sure why I still feel compelled to step in and 'help,' to make explanations or move the conversation along. They can do it on their own, and I'm afraid that my efforts to ease things along will backfire at some point. I'm sure I'm not the only special-needs parent who frets about when to step in and when to step away, and I know I don't have the balance right yet. At any rate, the friend appeared to have fun, I know my son did, and I didn't see any real behavioral flags, which puts this one in the "Success" column as far as I'm concerned. And I'll keep working on that whole helicoptering thing, even though I really do mean well when I do it.
Mama D: 1, Paranoia: 0.