Again...not knowing the redbridge system... but
Age standardisation compares with how well other children have done..
Posted in the Kent section..
To those of you with children born in August- the way age standardisation works is that children are only compared with other children born in the same month as them. So if 25% of September-born children score over 120 in a paper (for example), 25% of August-born children will also do so.
The difference in raw marks needed to achieve the same standardised score therefore depends on the difference in actual perforance between the age groups.
So the 'standardisation, would also be affected by the performance of the cohorts in each paper.