Do you ever email your DCs class teacher direct? If so, how do you address them, and how do they address you?
If I write an email to DCs class teachers, I always write "Dear Mrs X" or "Dear Mr Y". It all seems quite formal I suppose, but the teachers never refer to each other by first name in front of parents, so I assume that they don't want us to either. Letters and emails from school are signed "Mrs X / Mr Y", and nearly every teacher writes or speaks to me as 'Mrs Knight'.
Apart from one, who writes 'Hello my first name' or sometimes 'Hi my first name'. Then she signs off 'yours sincerely, Mrs P'. I always address her as 'Mrs P' if I write back.
It is a silly thing to worry about really, but what is the etiquette here? Do teachers usually address parents by their first name? If she signs off 'Mrs P' then it seems wrong for me to write 'Hi her first name' back. But the fact that she uses my first name but only her surname makes me feel as if she's treating me like one of the children. Perhaps she is! 
Maybe I'll just stick to face to face communication
or stop worrying about tiny things