Hi Shnoz,
Hmmm ...
I am usually loathe to comment on cosmological issues or matters of deep physics because I am woefully under-quallified and frankly it gives me bad headaches but ...
According to the current standard model space-time is as much a creation of the event that brought all the matter/anti-matter and the laws of physics into existence in what we refer to as the "big-bang". ie space-time came into existence with the big bang. There was no space-time before the big-bang.
Therefore, as I understand it, there was no "time" and no "before" the big-bang -- time did not (and could not) exist until the big-bang brought it into existence. There is no before, only after.
How can something come out of nothing? Hasn't your Physics teacher heard of quantum theory? Vacuum polariszation? Perhaps he is uncertain about it?
Alex hit the nail on the head (see above) with his comment.
Best,
Les D