As to the comprehension, his not finishing it may mean he was more careful with the questions he did answer. If a child is weak at comprehension, there is no point in their bombing through the comprehension in order to finish as they are more likely to write rubbish.
I just tell a little story
to confirm what fm has just explained. My DS is only in year 5. At his last comprehension test day in November at school, I was rather unhappy when he told me he didn't have the time to finish his test. He was telling me, that few of the chidlren in the class did finish it... Well, you never know what that means, do you?
that could be half the class, or a quarter , or four out of 30?
But my DS, for having done his best , had missed out at least two of the last pages!!!
Well, the day of the results came and it turned out that my DS has been in the same band as the ones who had finished (except one): so he did indeed do his best and marked as well as the ones who had rushed to finish!
I hope it lessen your worries...
For the maths at kes, as fm explained, the last questions are very though: the headmaster explained at the open day that he himself wouldn't be able to answer them. I was surprised by such a staement, but interpreted it as a way to stress the high level of complexity of these quesrions. These are here just to find out the happy winner(s?) for the scholarship.