Wikipedia has a many a word on this subject eg.
A-level
Between 1963 and 1986 A-Level grades were awarded
according to norm referenced percentile quotas (A <= 10%, B = 15%, C =
10%, D = 15%, E = 20%, O/N = 20%, F/U >= 10% of candidates). The
validity of this system was questioned in the early 1980s because,
rather than reflecting a standard, norm referencing may simply
maintain a specific proportion of candidates at each grade. Which in
small cohorts can lead to grades only indicating a candidate's
relative performance against others sitting that particular paper, and
so not be comparable between cohorts e.g If one year only 11
candidates were entered for A-Level English, nationally, and the next
year only 12, how can you be sure that the single A awarded in year
one was equivalent to the single A awarded in year two. In 1984 a
decision was taken, by the Secondary Examinations Council, to replace
the norm referencing with criteria referencing, where grades would in
future be awarded on Examiner judgement. The criteria referencing
scheme came into effect in June 1987, and since it's introduction
Examiner judgment', along with the merger of the E and O/N grades,
from June 2002, has increased the percentage of A grade awards from
10 to > 25%, and the A-E awards from 70 to > 98%.
similarly:
GCSE
In September 2009 and June 2012, The Daily Mail and The
Telegraph respectively reported that teenagers' maths skills are
no better than 30 years ago, despite soaring GCSE passes. The articles
are based on a 2009 paper by Dr Jeremy Hodgen, of King's College
London, who compared the results of 3000 fourteen-year-olds sitting a
mathematics paper containing questions identical to one set in 1976.
He found similar overall levels of attainment between the two
cohorts.[38] The articles suggest rising GCSE scores owe more to
'teaching to the test' and grade inflation than to real gains in
mathematical understanding.