Simple rule. If I don't have a solid enough friendship to ask about their bowels or their pelvic floor then I don't ask about their kids' exam results.
What I'll say myself in 5 years time? Probably the truth, simply and concisely, and then change the subject. It has served me very well through the 11 plus debacle (still ongoing - everyone currently wishing to share a story of some friend of a friend who got whisked off the waiting list in the last days of the summer holidays.)
Now the thing that really does puzzle me is that when exiting from school some children from older years sometimes ask my reception child which colour book box she reads from. I assume though that it is polite conversation because we are passing the book boxes at the time and it is just a friendly bit of small talk which they deem relevant at that point in time.
Hmm ... if you assume that then you are verily as green as you are cabbage looking.
Reading book competitiveness is a nightmare at most primary schools and I must confess that I myself have been guilty in the past. Many years ago, when I discovered that a child with more than moderate learning difficulties who went to 'Posher Postcode Primary' was on the same reading book as my 'able table' DD at 'Scruffsville Notice-To-Improve Infants' I kicked up a considerable stink.