Can I join? DS is PDD-NOS and is currently attending all day school in the PPCD program, but spending some time in the mainstream K class. He eats lunch and does specials (art, music, PE, library) with the K kids and is spending about an hour a day in the K classroom as well. He has had obsessions also. Trains have been one for the past 2 years, and now we are way into ice (as in the movies Ice Age and Happy Feet), icebergs, ice melting, geysers, penguins, brief one with skunks, grass growing, the sun setting and coming up on the other side of the world, etc. I love it as it makes him unique! Typical conversation when he gets off the bus...
Me: "Hi Matthew! I am so glad to see you! I hope you had fun at school today!"
Him: "Mommy, there's a geyser field here!" {makes geyser noises}
Me: "Cool! Look out! Was your friend W at school today?"
Him: "Mommy, is the grass still growing here?"
Me: "Yes, let's go in now."
His imagination is amazing too...I love how he builds "icebergs" with his megablocks, then they fall down when they melt.
The anxiety issue...I think Matthew experiences this sometimes too. He was telling me last night that he was sad at school because they "left me behind". I think it was because the aide was not "right" next to him for a few minutes in the K classroom. He does not seem to be losing sleep over it, but is getting upset at school. I did hug him a lot and explained to him that if he is scared or worried about something he should tell his teacher because they don't want him to be sad and will help him. I can sympathize because I too dealt with the anxiety issue as a child, and I remember laying awake at night worrying about stuff. Sometimes things like was I going to get lost at my new school, was I going to do okay on my test, was I going to make any friends (always hard in a new environment for me), etc. I think the best thing you can do (which I am sure you already do) is to reassure him that you love him no matter what, you are always there for him if he wants to talk about anything, and come up with ideas of things he can do to cope. Like for me, having my mom remind me that I can always ask a teacher if I got lost, and no they won't get me in trouble for being lost did help some. I always wanted to be the "good" kid who was praised by everyone and any criticism got me upset (I still struggle with that to be honest!).
Does your "quirky kid" get any type of therapies? Mine is in OT once a week to help with writing, muscle strengthening, and getting him up to his age level on fine/gross motor skills. He started 9 months ago and was not dressing himself or writing anything, and now he lays out his clothes the night before, and dresses himself down to his shoes, as well as is writing all kinds of letters and numbers!

He also gets speech at school to mainly help with him learning the art of conversation.