Quote Originally Posted by Оля
Thanks, Ken and Paulb.
How do you find this sentence:
The exact moment of his appearance in our school was when all this story started.
Usually we would only talk about an exact or precise moment if we were talking about two different events that happened at the same time:

He arrived at the exact moment when my car quit working.

Since you are comparing an event and "all of this" I wouldn't use "exact moment".

Better:
All of this started right when he arrived at school.
or,
This all started as soon as he arrived at school.
or (if you are talking about something bad),
The moment he arrived at school this whole was when this whole mess got started.

It is ok to say: