If Reisender's anectdote took place in an Elementary school, then what I have said doesn't apply, but considering that the student was apparently being asked to spell a word, I'm guessing it was at a point where they were supposed to know the alphabet, and that means knowing that the letter Z is called "zee" in English, not "zetto."
A typical Spanish teacher won't let a student spell "gato," as "gee, ay, tee, oh," so why should an English teacher let a student spell "maze" as "emu, ee, zetto, ii?"