Agree with mb, I think correcting 3 or 4 spellings in a piece of work is enough. For example, ds1 is doing a piece of creative writing at home (his choice) - he is retelling the story of Beauty and the Beast, but including himself as a character. He is 6. The language he is using is fantastic (though it might be cribbed from the film) - things like 'he had no love in his heart', 'Disgusted by her rags he sent her away' etc. Spellings are interesting to say the least - 'carsle' for castle, 'onse' for once, 'prins' for prince. But what he's writing is fantastic. If he were to do that at school, and it came back COVERED in red pen and spelling corrections, it would be SO demoralising, and I can imagine next time he would stick to safe words, like 'he was bad' 'she was good' rather than experimenting with adventurours language. He's also working very hard on improving neatness, finger spaces, capitals, full stops.
But if at the end of the piece it said something like 'Excellent writing, well done on your finger spaces and some lovely language. Try writing the word 'once' and 'prince' - look at the 'ce' sound at the end, then he would be more likely to remember them, rather than 'Good. Spellings - Once Time, Prince, Castle, etc etc etc'
I teach piano, and if a child brings a piece they've practised, I don't stop them at every mistake, I always let them play straight through first time, then we might work on one section, or we might think about the whole interpretation etc.
Agree they should have got 'there' right though!