Thanks mum10, for clarifying.
Interesting to see this is allowed. Goes to show that parents who would wish their children to practise in this way, are helping to bump up the figures of children 'who sat the exam on the day', therefore parents trying to deduce chance of there child getting through could in theory reduce this figure by say 5% for example. Also presumably helps those children at the top of waiting lists
I suspect this would be more the case in Bucks and Slough, as they generally have more grammars.
The only other factor to consider is if you didn't list the schools you are sitting 'practise papers' in and passed those, but didn't pass the test for the your chosen grammar