Well hopefully I can give some information on what the typical classroom arrangement is. Typically in non-lecture rooms in the older building on VT (Such as Norris) the teacher, as well as a black/white board is next to the door with rows of chairs facing them. In the lecture rooms typically it is opposite of that. Either way, unless one were to go plowing through rows of Desk-Chair combinations (Avg 30lbs or so) WITH PEOPLE IN THEM, towards the door, there is no way for them to rush the shooter.
Additionally, you also need to remember that the shooter was dual wielding pistols with extended mags. If they were 32 round clips in each gun, that would be 64 bullets. That means there were at least 2 bullets for every person in the room. Since he had thought this through, we could also make the assumption that he would fire one at a time, and then the other while reloading the other or at least attempting to reload it.
The construction is because not to far away from Norris is, McBryde Hall- A Math building where they are working on the steam pipes that run beneath the campus. Furthermore, there are pile-drivers and other heavy machinery for the construction of the new building a few feet away from that. The construction would be very very audible from Norris and might sound similar to a gun shot.
Given these circumstances and obstacles, there is absolutely no way, barring the exceptions of students standing or what not, that they could have rushed the shooter.
Finally, as for the mental situation, it depends on who you are. I have seen a lot of people saying that "this generation is softer" or what not. I don't care what generation you are from, survival instinct and the element of surprise will ALWAYS come into play.
If I were in that room, I like you, would like to think that I would have done everything in my power to protect my friends- even if it would have cost me my life. But since I was not in the same position that they were in, I can't accurately say that I would.
I would also like to say, that in some lecture rooms where he almost went person to person, that is really the time I would feel helpless. You can't play dead, you can't shut the door, you can't get to him fast enough.
In any of these situations, it would take incredible poise, and on the spot thinking to handle the situation. To say, "I would do this (Even if you have had a life or death experience) is irrelevant because you weren't in that exact situation)
-Kevin