Being a college professor, and very familiar with the system, I personally would not allow
vaping in my classes. It might technically be legal, but like cell phone usage and general chatting, it would be disruptive for the rest of the students. They would get distracted by it. If your teacher allows it, fine, it's their course. But I would not, myself.
Of course, if a student were in the back and occasionally stealth vaped, and was not detected, it would be hard to stop. But then I would think the student was paying more attention to their vaping than my lecture. In general, I wouldn't do it if I were you.
Just vape up good before class time, and you will likely be fine the whole class. Nic absorption is slower and more sustained than with analogs, so your nic levels will probably be more tolerable by vaping before hand than smoking anyway.