Somebody pointed me to an article from the Guardian in which Michael Rosen highlights how some school heads exclude pupils from GCSE examinations by losing them in the GCSE year. Unfortunately, a system that depends on published high-stakes tables will always promote effort into cheating the system for the sake of good results. https://www.theguardian.com/education/2016/nov/01/justine-greening-headteachers-underachieving-kids-data-michael-rosen
Other questionable practices include choosing easy qualifications like the European Driving License (a computer qualification), selecting qualification boards that are known to be easier than others, focusing on the GCSE year at the expense of other years, setting up free schools to do better for low achievers and thus excluding them, working hard to persuade parents who have less able children to choose other schools, and even concentrating on the top sets at the expense of the lower sets, which are in effect written off. The list goes on.
What is forgotten in all of this is that the wealth of a nation is the total skills and knowledge of all its population, not just the few who are pushed through a questionable examination system.