My oldest son hand writing came easily, my youngest not so much, LOL.
At 6.5 he was doing one or two words a day, that was it 🙂 Now at 7 he can copy words for about 5 minutes and do maybe 12 words in that time.
I would not worry about it at this young age, I would do as you are thinking, chalk board, sand, bigger movements. 6.5 is still pretty young with plenty of time 🙂
You could also do other fine motor skill activities such as building legos or other building activities that require small pieces. I think that helped out my youngest a lot because the hand eye cordination required and it was something he enjoyed too 🙂