Theory:

     Tommy looked at her with very superior eyes. “Because it’s not our kind of school, stupid. This is the old kind of school that they had hundreds and hundreds of years ago." He added loftily, pronouncing the word carefully, “Centuries ago.”
 
     Margie was hurt. “Well, I don’t know what kind of school they had all that time ago.” She read the book over his shoulder for a while, then said, “Anyway, they had a teacher.”
 
     “Sure they had a teacher, but it wasn’t a regular teacher. It was a man.”
 
     “A man? How could a man be a teacher?”
 
     “Well, he just told the boys and girls things and gave them homework and asked them questions.”
Explanation:
  
Tommy was looking at Margie with proud eyes because he knew something that Margie did not know. He said that Margie didn't have common sense because she did not know that years ago, the school was not the kind they had. Tommy wanted to put pressure on the time and said that hundreds of years ago, the school was not like the ones they had.
 
Margie was uncomfortable at Tommy’s conduct, and she said that she did not know what kind of schools they had centuries ago. She looked over Tommy’s shoulder, trying to read the book and said that whatever they had a teacher. Here, Tommy is mentioning to a machine teacher as a regular teacher because that is what they are used to.
 
Tommy said that it wasn’t the machine; it was a man (human being) who taught them.
 
Margie could not believe that a man could be a teacher because she had always seen a machine.
 
Tommy Tells that the man who taught the class talked many things with the students, gave them homework, and then asked them different questions like their mechanical teacher.
 
Meanings of difficult words:
 
Numbers
Word
Meaning
1.
Loftily
In a superior way.
2.
Regular
Normal; of the usual kind.
Reference:
State Council of Educational Research and Training (2018). Term-1 English Standard-9. The fun they had - Isaac Asimov (pp. 150-153). Published by the Tamil Nadu Textbook and Educational Services Corporation.