When I was at university, it would always annoy me when a fellow student interrupted a professor's lecture to ask a question or make a comment. I was paying money to hear the professor's words, I thought, not those of some empty-headed whippersnapper. Although I'll probably never sit in a classroom again, I was recently pleased to read this, from Plutarch, On Listening to Lectures
42 F, tr. Frank Cole Babbitt):
Now the person who comes to a dinner is bound to eat what is set before him and not to ask for anything else or to be critical; so he who comes to a feast of reason, if it be on a specified subject, must feel bound to listen to the speaker in silence. For those persons who lead the speaker to digress to other topics, and interject questions, and raise new difficulties, are not pleasant or agreeable company at a lecture; they get no benefit from it, and they confuse both the speaker and his speech.
δεῖ γὰρ τὸν ἐπὶ δεῖπνον ἥκοντα τοῖς παρακειμένοις χρῆσθαι καὶ μηδὲν αἰτεῖν ἄλλο μηδ᾽ἐξελέγχειν· ὁ δ᾽ ἐπὶ λόγων ἀφιγμένος ἑστίασιν, ἂν μὲν ἐπὶ ῥητοῖς, ἀκροάσθω σιωπῇ τοῦ λέγοντος (οἱ γὰρ εἰς ἄλλας ὑποθέσεις ἐξάγοντες καὶ παρεμβάλλοντες ἐρωτήματα καὶ προσδιαποροῦντες, οὐχ ἡδεῖς οὐδ᾽εὐσυνάλλακτοι πρὸς ἀκρόασιν ὄντες, ὠφελοῦνται μὲν οὐδέν, τὸν δὲ λέγοντα καὶ τὸν λόγον ὁμοῦ συνταράττουσιν).