I would ask:
How do you make sure that every child works to their own ability (especially if the classes are large and mixed ability)?
How many adults do you have in a class? Is at least one of them full time? (I agree with the other poster about job shares, although DD1's class has two part time teachers and two full time TAs, which seems to work OK).
What are your value added results (much more important than SATs, because they take into account the baseline ability of the children when they arrive.)
How much time do they spend playing outside? (because they will be very keen to tell you about academic performance - but do thay also allow the children out to be normal, lively, active children, make friends and let off steam).
And then I would relax, have a look around and see whether you think your child would fit in and thrive. And remember that the overall results for the whole school are, to some extent, irrelevant. You just need to know that YOUR child will achieve their potential there. And IMO they will do that best if they are happy, engaged and interested, but not hot-housed.