Yes, we did with my DS. His handwriting is absolutely shocking.
I think there are 2 main reasons - 1 is that he is ambidextrous and we think he probably should have learned to write with his left hand, but always picked up a pencil/crayon in his right. He would be seen as right-handed but does absolutely everything else with his left hand (would hold a tennis racket/10-pin bowling ball/hockey stick in his left hand, uses scissors in his left hand and would just naturally go left over right if he was picking up a heavy bag). He naturally picked up a pencil in his right hand as a toddler though and we never questioned it until he was much older but I do wonder if it’s not his naturally dominant hand.
The other reason I think is that he was taught 3 different ways to write by the time he was in his first year of primary - ball and stick at home (he was an early reader/writer), lead-outs (flicks at the end of letters) in his nursery school, and then lead-ins and lead-outs (flicks at the start and end of each letter) in P1. I think it just messed with his brain and I know that a lot of early years teachers (inc the nursery staff at the school he was at for P1) are very opposed to lead-ins and lead-outs at an early stage as it’s too many movements for that age of development in terms of fine motor skills.
His handwriting got progressively worse and then when we lived overseas we took him to a handwriting specialist who said that the best thing for him was to develop a style and stick with it - practicing every single day until his brain developed new neuro pathways and it became natural to him. The school he was at overseas taught cursive (proper old style cursive - not just joined up) and that seemed to click for him. His writing was never beautiful, and it was always very small, but it was certainly legible.
We then moved back to the UK and he was bullied in class for the way he wrote (he was in a school that did not care one bit about handwriting and was generally pretty low achieving), and he also got frustrated because it was slower to write than he wanted (his brain moves far quicker than his hand) and it slipped back into old habits. We encouraged it at home but it was too late by then.
He did 4 essay-based A-level subjects and it was a constant worry about examiners not being able to decipher his writing. Somehow he got away with it and he’s now at uni where everything is typed. I suspect his handwriting will get worse and worse now because he writes so little.
If you can get to a handwriting specialist - do it now! It’s not too late but it soon will be, and be warned that it takes a lot of dedication - daily practice for many, many months