Ответ:
1) John was a very intelligent ( or clever/smart ) boy.
2) Jon study at the very famous private school.
3) John used abstruse (заумные, трудные для понимания) words, for example: narration, extinguish.
4) Because John's mother wanted to sound like an educated woman In order not to disgrace (опозорится, пристыдится) in the eyes of the teacher.
5) She cooked home-made cake, and treated (в этом случае угостить) the headmaster with tea.
6) Because dog excited by the smell of the cakes.