Depends on the purpose of the activity. During writer's workshop - sound it out, keep going. Don't sit with your hand up waiting for me to come spell a word for you. If it's science or social studies writing we've probably made a word splash together on the board with the key vocabulary which they can copy into their writing. If the child is clearly frusterated, I usually spell it - some things just aren't worth it.
I always spell it for them, unless it's a spelling word or something like that. Chances are if they encounter it again, they'll spell it right the second time.
Also, I LOVE the idea of the word box! Great idea for when students are writing independently!
I have a mini-lesson on how to use the dictionary to help you spell a word correctly. I make them use the dictionary for spelling and for definitions of words they come across.
I usually sound it out for them, but not with the right syllables. So "acceptable" becomes "ac-cep-table." And sometimes I give them the first three letters and tell them to get the dictionary.
