Thanks for the responses!
no5no5: Kai's not having meltdowns at Preschool about this. This is possibly because they're only working on learning the alphabet, recognizing (only) their names in print and starting to write their names. He's obviously at least a little beyond that stage, and is probably quite confident doing the Preschool's activities.
The issues are all arising here at home, throughout the day at random intervals. He chooses how he'll fill in his time and that seems to be part of the problem. Yesterday after hearing a family member was sick, he set about making a card. He drew a great picture of an Autobot on the front, then wrote "Get wel soon, lov Kai". After staring at it for 5 minutes, he totally destroyed it. According to him, there was something wrong with the words but he couldn't work out what, rendering the card useless.
The biggest recurring trigger is however, instructions. If there's any sort of diagram, he can pretty much do it but when there's only text - BIG problem. At the moment, he's fixated on creating an online character for a game he likes to play (age range stated as 7-10yrs). It's positively killing him

mnmom23: I agree with your approach. Perhaps we need to focus more on previous milestones or made-up "what if" type scenarios (away from today's issues) to reinforce that asking for help is not a bad thing.
JJsMom: Along the lines of your experience, we thought soccer might be fun for him as he loves to play at home. Unfortunately, the closest Kai would go to the playing field was the gate outside the grounds! Still working on trying to find something he'll at least have a go at.
Thanks again for your replies, and if anything else comes to mind, I'm all ears.