Do you have to feed the whole class?
If it's just for a tasting or just for you and perhaps one other person, use a thermos bottle. That's what they're made for.
If it's for the whole class, after you get to class, use your crock pot and set it to the lowest setting, usually "warm", and after 15-20 minutes, turn it off. The ceramic liner will keep it warm for quite a while.
"Food is our common ground, a universal experience." - James Beard