Schools with disadvantaged intakes are less likely to be outstanding as they are harder to run, thus Ofsted grades should not be used as a judgement of headteacher effectiveness.
SAYS THE INCOMING CHIEF OF OFSTED 
www.tes.com/news/school-news/breaking-news/ofsteds-next-chief-watchdogs-overall-verdicts-schools-not-fair-way
Along with Sean Harford's letter confirming that multiple marking in various colours is bollocks and Ofsted don't want to see it, things look like they might be looking up, Ofstedwise?