I appreciate that this thread is a bit old now, but I would just like to add that there is a positive side to Steiner!
My now 17 year old moved there from another Edinburgh private school at the age of 14. The previous school is a well known and old established one - and was a total disaster for my child. We had no previous experience with Steiner, but it has turned out to be perfect (or as near perfect as a school can be) for us. I have two older children; one attended another Edinburgh private school, one a state school - so I do have experience of a variety of schools - and although Steiner has its ways, I am very happy with the education my youngest has received there. The staff that we have dealt with have been excellent, they have been very responsive to any issues that have arisen, and the support from a guidance teacher has been outstanding. The teachers all seem to me to be highly motivated; some have voluntarily left jobs in other, better paid, schools to come to Steiner.
I also know the mothers of at least two other pupils who moved to the school at about the same age - this time from two different state schools - and both love it, despite having long journeys in every day. Some of the parents that I know are actually teachers in state schools themselves, but still chose to send their children to Steiner.
The academic standards are high, the breadth of knowledge acquired is so different from the narrow focus of so many other schools, and the life experiences are great. The art department is fantastic, the science teaching is brilliant. The only thing that I know they don't do too much of is sport - they don't have the facilities. This is not a problem for us, but if you have a very sporty child you might want either to look elsewhere or to arrange your own after-school activities.
The Steiner buildings are far from smart, and trips, etc are always arranged as cheaply as possible - these to me are advantages, as I am so glad not to be involved in the highly competitive and expensive jaunts arranged by some private schools. The fees are actually pretty low compared to most Edinburgh private schools, and we are very rarely asked for extra money.
I have no experience of Heriot's or Watson's and am certainly not criticising them in any way, I just feel the need to stick up for Steiner sometimes - I think you will find people who have had bad experiences at virtually any school in Edinburgh, so it really is down to visiting schools yourself and deciding what would suit your child.