What are the big differences b/w UK primary and US (SF) elementary schools

Just curious about this. We've decided to move to SF where DH is originally from. Our DS would have been due to start Reception in 2013 here in London, so Kindergarten in 2014. I've already toured a bunch of schools here and while he's not in school yet, I feel like I have an idea of what the schools here are like. I went to American int'l schools, which are sort of a thing of their own. What are the big differences I'm likely to encounter in the state schools, given that I'm going from one urban area to another?

Things I've picked up from the internets seem to be: at least in SF you only get art/music/science if you get into a school with an active PTA, parental involvement seems a lot higher, very different start times for different schools, less recess, foreign language learning taken much more seriously (lots of immersion programs, etc.).

When you say SF, do you mean San Francisco?
And by 'state schools', do you mean the San Francisco public schools?

When you say SF, do you mean San Francisco?
And by 'state schools', do you mean the San Francisco public schools?

Yes to both.

hi i'm quite curious about this as well so hope you will get some responses.  i have a child who's in year 2 here and will go to 2nd grade next year in the states so am curious about what to expect.