I would agree with seeker about the attendance figures. The school I worked in had lower than expected attendance due to its intake, and remained stubbornly below the level generally regarded by Ofsted as 'requires improvement' - and we still rose a level when Ofsted came (from the old Saisfactory to the new Good [which remembering that the levels have changed so that what used to mean an Oustanding now means a Good wasn't bad going])
Ofsted looked very thoroughly at the figures over several years (down to our analysis of attendance by different groups etc), looked at everything that we had done to improve them, looked at the context of the school, and said that attendance was in fact Good in that context. So attendance alone, especially if there is a good 'story' about why it is low, wouldn't change the overall level.
I would agree with Mrz that a school in a difficult area getting Outstanding is almost certainly a 'better school' - in terms of quality of teaching and learnng, care for and focus on individual children, innovative practice - than many schools in leafier areas getting far higher results (in terms of exit grades) but similar or lower Ofsteds. Yes, the absolute 'exit grades' of the children would only allow a school with a different intake to get a Requires Improvement or a Good, but the actual 'what the school does to the children' in the school in more difficult curcumstances in order to get those grades will be much, much more and the Outstanding grading will reflect that.
I would also argue against the idea that it is 'easier' to get meteoric progress with children with lower starting points. Yes, a few of those children will be 'diamonds in the rough' - children who simply need goo teaching to move from a low starting point to a high finishing point. However, the factors that made their starting points low - little or no pre-school education or stimulation or conversation [we had children arriving with no spoken language, having never really conversed with by anyone in their pre-school years], no toys or books in the home, poor housing, low parental literacy, poor diet, lack of sleep due to unsuitable or inadequate housing, little or no experience of the world, parents who are absent or addicted to various substances, in prison or sleeping all day due to working all night (in the normal or 'night' economy), already being carers for even younger siblings, being cared for only by slightly older children than themselves, frequent moves around the country, no parental value placed on education etc etc etc - do inhibit the progress made by many such children, so if a school CAN get metoric progress from such a cohort they are doing very well indeed. And before you say that I am exaggerating - I have encoutered all the above (and more) in only a few years at a school with an only slightly 'interesting' intake. Colleagues who teach in genuinely 'rough' areas will have encountered much more.