As you spent roughly the same amount of time teaching that I did, Sherrardk, did you ever have identical twins in the same class? I did and I tried my hardest to stop myself from doing what nearly all of the other kids (and most of the staff) did, which was simply to address each of them as 'Twinny'.
I spotted that one of the boys had a very small chip in one of his upper front teeth, so I always tried to get a good look at their dentition before speaking to them and addressing them by name. My technique worked well until, in the same week, the boy with the chipped tooth had it repaired by a dentist, while his brother fell off his bike and chipped exactly the same tooth ;-)