Rosar, a school's perspective is dictated by Ofsted - these results are made very important both by Ofsted, the LEA and existence of league tables.
Poor results trigger questions from the Ofsted team before they set foot in the building - why are results poor? Is it the teaching? Is teacher assessment rigorous? Does it match work produced by children on a day to day basis? Why aren't able children achieving level 5? Why doesn't teacher assessment match test results?
Poor results trigger LEA involvement - advisory visits, SIP questions, etc, all asking the above questions.
Parents choosing schools for the following year often look at the league tables, and in a small school one child can count for 4/5% - a huge slide. Parents rarely look at the results for the last three years together.
All this is in no way justfiable because of one crappy, poorly paid marker. But it happens all the time.
As it happens, our work was fairly marked this year - for the first time in years and years, I will not have to sit writing reviews which have in the past altered our results by as much as 20%. Yes, that bloody matters. Fwiw, we are a school who teaches a broad and balanced curriculum, with no drilling. But we still have to ensure that our results are as good as they can be, and that the marking is fair and just.