Really bad student papers always make me uncertain: whether I, a non-native English speaker, is qualified enough to teach composition to Americans. I know that I'm not (necessarily) responsible for their poor performance. They are just lazy. They don't put enough effort to write early drafts. I know all this very well. But still, I feel somewhat hurt. Or, probably, I'm simply too tired to think straight after five hours of reading and commenting on these papers that, apart from a few exceptions, are not as bad as to depress me...
