England has 164 grammar schools, 85% of which are academies at liberty to set their own individual admissions criteria including the type of entrance tests they set and what weighting is given to each one.

The actual marks from these tests, referred to as raw marks, are never disclosed, instead parents are given Standard Age Scores (SAS). A standard score shows how well the individual has performed relative to the mean (average) score for the population although the term population is open to interpretation.

If a student scores 65% on a test, what does this tell you? Is this mark good? Bad? Average? If it is deemed to be a good/bad/average mark, against whom is this judgement being made – the other children in a class, in a school, or similar children across the country?

These fairly obvious questions are what led to the development of Standardised Scores; numbers which not only tell you how a child performed in a test, but also give you some information as to where their score sits within the range of scores recorded by other children who have taken the same test.

So, if a child scored 65% on a test in which the average child scored 70%, their score might be reported as a standardised score of ‘95’; if the average child scored 60%, their score might be reported as ‘105’.

If you know that standardised scores are created such that the mean score is allocated a score of 100, that two in three standardised scores are between 85 and 115, and that 95% of scores are between 70 and 130, you can make much more sense of a child’s test score reported as a standardised score than you can from a test result reported as a percentage or a raw score.