The use of correct grammer.

I have a question - There's a new principal at the school our children attend. Prior to the new principal our children - throughout the whole school would greet all adults with, for example "Good Afternoon Mrs .........".

The new principal now has the children greeting her by saying "Mrs ......... Good Afternoon"

I find this frustrating. Is there anyone that can inform me as to the correct way to greet someone, at an assembly for example. MN