I personally believe that all this standardisation of scores is absolutely unfair. At the end of the day, it is a test and the result should not be dependent on the month ( or minute!!!!!) the child was born.
OK. Let's take the most extreme example.
Take two babies. One born on 1st September 1999, the other 30th August 2000.
On the 1st of September 2000, which one is the most advanced 'educationally'? Can the one day old do anything more than pretty much reflex actions? Can it play with toys? Recognise a range of faces? Now ask the same question about the one whose 1st birthday it is on 1/9/00. Assuming that both have the same intelligence, normal birth & upbringing, the one year old will be one year more advanced than the new-born.
If this test was one by which the babies would be allocated schools later in life, it would not be fair on the new-born, as obviously the one year olds would win every time. Would this be fair? I bet that you will say that it isn't fair.
Come Reception class, do you remember parents complaining that their children shouldn't have to start until summer term because they were the youngest in the class, or heard teachers talking about the 'young ones' being less mature? Yet the young ones may be of the same intelligence as the older ones. Some schools with intakes of 45 will have a class of the oldest 30 Y1's, the youngest 15 Y1's with the oldest 15 Receptions, and then another of the youngest Receptions. They do it like that because the younger Y1's are closer in maturity to the elder Reception children.
Move forwards 7 years to the 11+. The difference in ability due to age still exists, but to a lesser extent. It is still there, and measurable. Would the child one year older still have an advantage over the younger one? Yes, of course - it's been alive for 1 more year, even if they are in the same class.
The standardisation is what allows children of the same ability to be judged against each other, irrespective of the month they were born. That's fair. Not to have standardisation would be unfair to all but the eldest children.