When DS1 took the CSSE test at SHSB in 2007, I just took him there, left him when told to and came back to get him at the appointed time. Probably reminding him for the n
th time that it would be a good idea actually to answer all the questions (he didn't, but still passed). I don't think I even thought of the possibility of disruptions, and he didn't mention anything untoward.
DD sat the test at SHSG last November; this time, older and wiser / more cynical, it did occur to me to warn her that there may be disruptions (either inadvertent or deliberate attempts to put other children off); in the event, she said that she hadn't noticed anything.
However, speaking to some other parents later, I did wonder whether she and I had actually been in the same place as them and their DDs. I arrived slightly late to collect DD, thus many girls were already coming out of the school as I walked from the car. One of my first thoughts was, Oh good, most look at-least-reasonably cheerful, it can't have been too bad. Apparently like DD, though, I completely missed all the weeping, wailing and general total distress that everyone else had experienced / observed
As for rewards - DS1 was not promised anything but I did get him a book in WHSmith while he was in the exam. DD and I may have discussed openly where we were going for lunch after her exam (nice Thai place near home, which happened to have a £9 a head Winter Special offer on as it turned out) but I would hope that hearing of this wild excess would not have had an adverse effect on other DDs. Neither of ours was promised anything should they pass.