Speaking of children and teachers, when I was in primary school, we had quite a few repeated names.
We had three Carlos, two Martas and two Ivans. Most teachers didn't have any problems: the Carlos got each called by their surnames, one Marta had a middle name and the other didn't, so they were Marta Maria and Marta Surname and the Ivans were actually Ivan and Iban, so pronounced differently (or we just called Iban by his surname, since he actually got enrolled in our group later than the other)
And one year, I think I was seven or eight, we got a substitute teacher, and the name problems started... with me. Not with any of the repeated names, that would have been sort of logical.
My name is Almudena. That's it, that's my whole legal name, no middle name, no first name with Almudena second, just that. It's a very long name, so everyone called me Almu.
She called me Maria, got mad when I didn't answer to Maria, and told me to start getting used to put my full name on all my exams and homework "as you are going to need to do in high school and college"
Ok, I told her I was already doing that, I signed everyting with Almudena FirstSurname SecondSurname.
"That's not your full name! You have to put Maria de la Almudena FirstSurname SecondSurname!"
"But I'm not Maria de la Almudena, I'm just Almudena"
"You can't be! That's not a name! Since it comes from the Virgin of Almudena, it has to be Maria de la Almudena"... Repeat every day until I actually got the school secretary to show her a copy of my birth certificate, and she still had more to say. Between that and some other things, we were glad when our normal teacher came back.