DD is 6. The name on her birth certificate is the full version of a name but since birth she has been called a shortened version. It’s not this name but think along the lines of Margaret and Maggy.
We managed to navigate reception fine. There are two ‘Maggy’s’ in the class but the teacher would use Maggy A and Maggy B. All paperwork at school says Margaret known as Maggy.
For some reason, the Year 1 teacher has decided she wants one Maggy and one Margaret and my DD has been selected to be Margaret. It’s not what we wanted her to be called! It’s seeped in to wider society now and we can’t walk through the village with out someone shouting ‘Hi Margaret’.
Should also add it’s not the only name that’s doubled up in the class but only my DD has been renamed by the teacher. 
So AIBU to speak to the teacher? My DD is confused and doesn’t understand why I won’t call her Margaret. Or am I being precious? Should add that teacher managed to use Maggy all through parents evening which leads me to believe she understands it’s not really on.