The Australian Transportaion Safety Board in their human factors course spend a full hour trying to explain situational awareness. This is a lecture by a trained aviation psychologist at probably the finest accident investigation body in the world, how you are supposed to do it in 20 minutes is beyond me!
That said, the crux of their discussion was that situational awareness involves knowing where you have come from, where you are now and where you will be in the future. Simplistic but true. The difference between surface vessels and aeroplanes is that we in aviation have to keep all that in mind in three dimensions not two. Therein lies the problem.
Good luck with the lecture!