I don't think it is always writing with the left hand that produces writing problems, I think sometimes it may be a brain wiring issue.
When I taught special ed, both righties and lefties (and lefties who had been taught to write right handed) often had problems with writing (neatness and spacing) some also had communication problems or visual orintation problems.
There has been some research that links poor handwriting to speech and language delays as producing language both written and spoken uses similar parts of the brain. There have also been links to visual impediments.
Astignatism that can manifest without other sight problems will also interfer with depth persecption and the ability to distingish between horizontal and vertical lines. This can cause poor motor skill which include writing.
Not saying that these are the reason your son has poor writing but I encourage you to not blame it on left handedness, and to explore other problems that could contribute. Does he have a speech or language delay, does he have astignatism, are his other motor skills poor? Check it out because if you have another factor other than left handedness it can be corrected.
