I've always had a bit of theory that if you have a surname that begins with a letter in the top half of the alphabet you have a slight advantage in life.
As regards Primary schoools, I help out at the school and things are often done alphabetically. With the As and Bs you are not in so much of a rush when you listen to them reading etc, they tend to have more of your time. Not lots more but marginally more.
You may look at your watch, know you have limited time and need to hurry through the next 5 or so readers (further down the alphabet). Of course you try to apportion time fairly but this can happen.
When it comes to activities and special treats often again the register is used as a guide. Those with surnames in the early part of the register get to go first. This can build confidence over time maybe? In my school we had very confident children with the surname Aitken, Allen, Appleton Bell and Collins!
My surname fell at the end of the alphabet. I can still remember the rare times the teacher decided to work through the register in reverse order, with the Zs first! I remember I missed my go as I was away from school that day!
I also remember (when older) sulking at the back of the exam queue waiting to go into the examination hall with the Ss, Ts and Ws! It took an age.