Rather than continuing with the 'problems with education' tangent in the other thread I thought I'd start this thread (warning - this is a teacher's perspective).
Someone mentioned their teacher friend who would not correct a spelling mistake because it was a piece of maths work. Let me put this into context.
Johnny has always struggled at school, as a result has very low self concept as a student and gives up on tasks very easily. He is used to getting all his work back covered in crosses and red writing. But Johnny has started to realise he's more capable in mathematics, he's slowly gaining confidence, and this confidence is starting to spread into other areas of study. If the teacher were to cover their maths work in red corrections due to spelling mistakes, Johnny wouldn't even see the fact that most of his 'answers' have ticks. Trust me, the most kids will just give corrected work a quick glance over to see if they've done well, ok or bad.
Scenario 2. Mary thinks she's stupid. Whenever she's asked to write anything she has so little self-belief that the teacher is lucky to force two sentences out of her. One day Mary is set a creative writing task on a topic she loves - and the writing just starts to flow. Before anyone knows it she's up to half a page. There's barely any punctuation, half the words are spelt incorrrectly, but it's a great story and she's really put herself out there and taken a risk with her writing that she wouldn't normally do. Would you send this piece of writing back covered in red corrections? Potentially scaring Mary off from ever trying again? Me, I would make some punctuation corrections essential to the flow of the story and then talk to Mary to explain that yes, there are lots of spelling mistakes, but that I chose to leave them as her efforts on this story are amazing, best work this year etc etc.
Finally, by the 32nd writing book, sometimes the teacher misses some spelling mistakes!