why do English lit teachers ask you how you feel about a poem and then mark your answer wrong. my son read a poem and answered wrong?

You didn't actually say how old he is, so I can only assume around year 10 onwards?

It shouldn't just be marked wrong, is the mark not a percentage; say like 40% or something? Did the teacher not leave any comments??? That means there's a basis there that needs to built upon. I was always told in lit (although this opinion does vary) that as long as you can justify your argument with reasonable evidence then it's not wrong (not necessarily 'right' either though). Instead of complaining about it, in order to improve you need to find out exactly what the problem is.

Was this an essay? Because that's what I automatically assumed, but re-reading your question makes it seem like it's more of a short answer thing. Anyway, my guess is he didn't go into enough depth and wasn't analytical enough. Literature is a very analytical subject, every statement should be followed by a 'why?'. If that why isn't answered then you're going to lose marks. You also need to be specific in other areas such as specifically WHO the intended audience e.g 'early 17th century working class women' and so on. Nothing can be vague.

So when asked how you feel about a poem (assuming it's a short answer?) you cannot simply say "happy", even if you add in a few more words to extend the sentence. You need examples from the text to specifically show why, you could even talk about the feelings the author wanted to portray to the intended audience and so on.

I used to think english lit was the dumbest subject ever, but in my final year of high school I began to really love and understand it. It ended up being my best subject :)