Money would be my first reaction to your pros. and cons. There is a big difference in forking out £10,000 a year (poss. more depending on area) and not!!!
Having said that we moved our dd in Year 2 to an independent and haven't regretted it for one minute (year 3 now). However, I am well aware that a good state school would probably provide us with what we are paying for - but locally the state schools are not really up to the mark.
I would suggest you check out your local state schools first, but take no notice of 'outstanding' it means diddlly squat to be honest.
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The differences we have found are 10 less students in the class, quieter working environment - the kids tend to enjoy working hard and achieving and it is 'cool' to be good at stuff (the opposite was at her state!). Subjects like, Science, Art, IT etc., are taught by specialist teachers. PE is three times a week, not once in the hall, but hockey, netball, tennis, dance and swimming once a week. In the IT suite each child has a computer, no sharing between two. There are lots of other things that are also different, the structure of the work and the reading progression seems faster, with a new book each day if they want. They also seem to fit in more in the day and do lots of fun extra currliculum stuff, visits each term, not just once a year, visiting theatre groups, authors, talent shows, music concerts etc. etc. ...Generally the 'can do' attitude that anything is possible and you can do want you want to do in life if you want it is the biggest change and our dd is now 'buzzing' with it all.
A good state school can provide the above and if you have one near you then lucky you. Personally, I am glad she is now getting a work hard ethic and a good basis in all subjects up to Year 6, rather than leaving her at her old school and then moving....for one thing I don't think she would have been at the same level by then, as she was switching off and becoming disillusioned with school (at 6!!!!!). However, if we did have to move her now in Year 6, I think she would be OK anywhere with the skills, attitude and confidence she is gaining.