John Clare quoted this wonderful example of the frustrations of teaching...
Then Jesus took his disciples up the mountain and, gathering them around him, he taught them saying: blessed are the poor in spirit, for theirs is the kingdom of heaven; blessed are the meek; blessed are they that mourn; blessed are the merciful; blessed are they that thirst for justice; blessed are you when persecuted; blessed are you when you suffer; be glad and rejoice for your reward is great in heaven.
Then Simon Peter said, 'Are we supposed to know this?' And Andrew said, 'Do we have to write this down?' And James said, 'Will we have a test on this?' And Phillip said, 'I don't have any paper.' And John said, 'The other disciples didn't have to learn this.' And Matthew said, 'May I go to the lavatory?' Then one of the Pharisees who was present asked to see Jesus's lesson plan and inquired of Jesus, 'Where is your statement of objectives?' And Jesus wept.
Quoted from Classroom Behaviour, an illuminating guide to good teaching by Bill Rogers, published by Paul Chapman.