Students file into class, teacher provides info-dump to move the plot forward, bell rings, students file out.
High school students or college undergrads troop into class and sit down. The teacher or professor will provide a necessary info-dump to move the plot forward, or there will be a bit of characterization business: The main character has forgotten to do her homework because she was too busy fighting vampires, the dreamy kid isn't paying attention and can't answer the teacher's question, the bitchy rival to the heroine humiliates her in front of everyone, the super-smart but borderline-autistic kid invents cold fusion on the blackboard, etc. As soon as the necessary business is done, the bell rings or the professor dismisses the students, usually with an admonition to read chapters 3 and 4 of the textbook for tomorrow's three minute-long class. Related to Rule of Conservation of Detail and Moving at the Speed of Plot. Primarily a TV and movie trope for obvious reasons, though it does occasionally happen in prose fiction and comics too.