My two pence worth is - if you feel your child may be unsettled in a state school, a steiner or montessori school may be really good. If your child has some additional needs, incredibly shy, or even just can't settle down with having reading and writing forced at an early age, great.
I was very interested in steiner - until we visited our local one last week. I really liked the kindergarten - apple crumble was cooking for snack (the kids had helped make it) and there was lots of crafts involving conkers and mud. Fab.
The school was shocking. There was a year with just ONE pupil (the others in his class had left for various reasons) and he took lessons on his own!!!! Dh and I thought that was appalling.
In the year 3/4 mixed class, the teacher had NO control over the kids who were talking over him. They aren't allowed to discipline them.
I don't like the fact that nothing governs the teachers - they just decide what to teach as and when. Also they have no plan for 'bright' pupils - apparently they won't challenge them any more, just give them more art to 'combat' the extra skills in math/science etc. Plus when I said ds could already count (he's 2.6) the woman was fairly horrified, and said they learn about numbers at the rate of one number a week in years 1 and 2.
I could see it fitting in well for someone who didn't fit into state school system, but for my counting, football loving (football isn't allowed) ds, I think he'll fit in okay at the state school I've picked for him.