I have just moved her in February. Te secondary schools are mixed I think. We are quite near Cherwell (in Marston) which is a good state scondary school I believe. Also matthew Arnold in Botley (used to be bad I;ve heard but is much improved I believe) Botley isn't too expensive for Oxford either.
Do you actually need to be in Oxford itself? Cherwell is North Oxford which I think is quite expensive ie probably more than £400k for a house. There are good schools in towns/villages fairly close to Oxford eg. marlbrough in Woodstock (my local school) and Bartholomew in Eynsham. Not sure about schools south of the city. Cherwell don't have a uniform which would drive me completely potty!