There is not a teacher in the world who has taught anything worth learning who at some time has not come in contact with a class of students who made them wonder why they had chosen teaching, instead of something a little easier like defusing land mines blindfolded.
There are some groups of students, for whatever mix of the 80 or so variables that go to explain a child's behaviour, who are just plain hard to teach.
And even though you might agree with Jan Amos Comenius' nearly four hundred year old call that "schools should not be places of torture nor slaughterhouses of the mind," you feel like you are in one!