I am afraid that I can only answer for how Park was in the 1980s! But I will e-mail my friend whose child goes there and ask for an update.
I loved my time at Park. My mother was one of three women who founded it. She had originally sent me to the nursery of Dartington Hall School which was on the same site and was also a progressive school. Dartington Hall Scool closed down and I went to the local CofE. Then my Mum and two others decided to start start a new progressive primary. I was one of the original 30 pupils at Park. Therefore it is very close to my heart. My Mum is now dead but I am so proud of her for having been involved in starting a school like Park.
I have no idea whether children can go part time - I don't remember anybody doing that when I was there, but that does not mean it was not possible. However, the school was very relaxed if parents wanted to take their kids out to travel etc.
We did have structured lessons once we were old enough. It was not a free-for-all. We had time for maths and time for history and time for art etc. But the timetable was fluid and the lessons were less formal than at a regular school. We called the teachers by their first names and they treated us as individuals with valid opinions and contributions.
When I was there it was very friendly. The parents were very involved. Some taught lessons (e.g. drama, art or sport), some gardened, some built a play area etc etc etc. All the parents were expected to get involved in the school community. The children were all very friendly too. I don't recall any incidences of bullying and there was definitley less pressure to conform than at a normal school. The school had a non-competitive ethos so there were no grades or tests or sports days.
Regarding support for a child with special social needs I am not an expert. At an informal level there was a lot of support as the classes were very small and the teachers very engaged. If a child liked to hang out with adults that was fine as there were always parents around - gardening or cooking etc.
When I left Park I was sent to the local comprehensive! I probably did find the first year quite hard to adjust to. I had no problems academically (I beleive I learned more at Park then I would have at a normal primary) but I was used to a very small and personal environment. I did settle down fine after a while, I transferred with several kids from my class at Park and we remained close. I am now nearly 30 and my two best friends are still girls I met at Park.
I will e-mail my friend to see if I can get more up-to-date info.
If you are really interested in finding out more I would call Park and ask if you might take DS to look around. My friend did this with her child, they spent a couple of hours a day there together for about a week. Then she let the child decide whether it was the right school.