In college, I see that some of the students who sit on the first bench just keep on smiling or laughing at every joke the teacher makes. Everytime! Even if it is not funny!
The closest word that I could find was obsequious. But I don't think it does the job here because those students are not that much obedient or attentive to appease the teacher nor I would say they are sycophants.
They just act so fakely in that little time in order to please the teacher even though after the lecture they would just not give a damn what the teacher was talking about.