This stereotype is just average. The best comparison is in the Lego Movie where they go inside Emmet's mind and Wildstyle says something like "There is nothing in here!" And that is the same for Pepto-Blando. They pay attention so well in class because there is just nothing shooting in the back of their mind. They rarely have any original thoughts, whatever they say just feels empty "Follow your dreams!" "Your beautiful just the way you are!" And they just believe everything any teacher says pretty much. They require a hive mind of average people just to think properly, a sensory comparison would be eating plain flour, flour is used in cookies which are interesting. But flour is plain and boring, not to mention bland.
All the pepto-blandos in class litterally drool on the floor during the lesson. Are they literally so smart because of how braindead they are? This teacher is not interesting in the slightest.