Translation:He had often called me his best student.
Obviously, since seine conjugated to seinen. I guess I meant why is it accusative? e.g.: he called me "a man" - would it be nominative, or also, Er hat mich "einen Mann" genannt?.
Isn't "mich" the accusative part of the sentence?
As Christian said, ‘nennen’ takes two objects in the accusative. In general, if two things are equated by a verb, German tends to use the same case for both. So ‘nennen’ gets two accusatives and ‘sein’ gets two nominatives.
Even in English what he called me would be the direct object, it is "mich" which is different from the English. In English "me" would be an indirect object, but in German certain verbs require both be accusative. I think G.P. Niers explains it well for me.
This is from Pons
"[jdm] jdn/etw nennen" = to name sb/sth [to sb]
So am I right to say that this is only used when we call someone else (other than the person we're speaking to) some names?
I think you're confusing infinitive of the verb to be, "sein" with the male possessive, "sein."
"Ich bin sein bester Schüler" is nominative. BUT "bin" is the first person singular form of the verb "to be" -- that's where "sein" comes in. The reason it's nominative is that the subject and object are the same thing -- equivalent -- because one of them IS the same as the other.
See "conjugations of the verb to be, sein" at: http://german.about.com/library/verbs/blverb01.htm
Less confusingly, "Ich bin der beste Schüler" is nominative for the same reason.
"Sie hat mich ihren besten Schüler gennant." is accusative, just like "Er hatte mich seinen besten Schüler genannt." The subject, pupil, is receiving the direct action of the verb, to be called.
He had frequently called me his best student. Isn´t this an acceptable tanslation?
Instead of "Er hatte mich oft seinen besten Schüler genannt. "
..can I say "Er hatte oft mich seinen besten Schüler genannt. " ?
German word order is different. I think a pronoun object usually comes right after the conjugated verb in a main clause or simple sentence. The time frame usually comes at the beginning of the middle section which would be right after that; then, why and then how and then where.
It does state that a short adverb of time can precede a noun object. The noun object in this case is probably considered to be a part of the ending verb
Then it does go on to say that emphasis would change with different word order, so I suppose it might be possible. Wouldn't it mean that "he had OFTEN called ME his best student. (sometimes he called other people his best student)? Often me, so other times not me? I hope a native speaker comes along to explain how this word order would be interpreted. I think in the regular word order "oft" affects the verb rather than the pronoun.
So, does "oft" count as Time and "seinen besten Schueler" count as Manner in terms of the Time, Manner, Place thing?
In the previous examples the person who was named after something was dative, here it is accusative. Is the difference naming/calling that takes dative /accusative?
There are different uses for "nennen" and some use Accusative/Accusative, especially calling someone something. Yes, "name your price" or "state your preference" takes Accusative. http://dictionary.reverso.net/german-english/nennen There is even a context for Accusative/Dative when you name a child after someone. (the preposition Nach takes jdm or Dative) http://german.about.com/od/grammar/ht/Dative-Prepositions.htm