Hi reallyhoping, which area are you in? Was it because of score or distance that you did not get offered a place?
If it is score then you will need to look at the qualification appeal info, if it is the distance the oversubscription. From memory (try using the search facility - I'll have a look when I've got the plumbers organised) - there have been discussions about prematurity in the past.
Sometimes it can make a difference even at this age, for example if they are in an academic year ahead of the one they would have been in if they had been born at term IYSWIM.
However it is quite difficult to argue too much down this line if the child has been doing well at school (which you will want to be arguing
) as being prem is not likely to explain why there is a sudden "blip" on the exam day, as you say there may be other circumstances to explain that..