Umm, what you are talking about is TEACHING not LECTURING.
Lecturing is where you drop the chief on the ampitheatre and the whole tribe comes to listen.
Teaching is where, once every 24 hours you drop the chief onto a child and they gain experience points

I don't think that you gain anything from lecturing, but remember Carla's video? It had this thing that popped up and said what the chief was doing. Maybe I haven't got that far yet...