Note: this isn't meant to tell you what you'll when Ofsted call, just to show you how the actual Ofsted grade distribution depends on things that a school can't control: its gender intake, its religious affiliation (or none) and its prior attainment. It illustrates the degree of bias in Ofsted grades as of 30 April 2014. There is a high degree of correlation between KS2 average points scores in 2008 and the Ofsted grades current in April 2014, after that year group had concluded their Year 11 examinations in August 2013. I think this is an indication of bias, and schools are not being judged fairly, given their different starting points.
Enter your school's details below and see how your prediction goes. I've only included the things you don't have any control over, so you can see how wrong it is that these should be correlated with Ofsted judgements.