The history of secondary school grades in the UK are a good example of why the top of the scale may not be the highest you can go.
Up until 1975, the highest score was a 1.
From 1975, the previous highest score was aligned to C, with grades A and B being higher. But, students taking the former CSE could still only get a '1' at best.
For students due to take exams in 1994, their coursework from 1992 was marked from 10 to 1, with 10 being the highest. It was felt that employers wouldn't understand what a GCSE grade of '10' meant, so letters were reinstated. However, early coursework had aligned 9 with an A, so a grade higher than this was required which resulted in the 'A*' being introduced.
Now, from 2017, the grades of 7 and 8 align with an 'A', and a 9 is an 'A*'.
So, in the context of this thread, 10 is as high as we go because that is the best race there has been. When a race better comes along, we can just add the grade of 11, or 10*.
