From my own experience, I would get an OT assessment and maybe a psychological assessment too. But like aeh, I am testing prone and have learned by experience that my evaluations of DD10's learning problems are often completely wrong. There is so much involved in writing, it is hard to get to the bottom of the problem on your own. There may be factors contributing to this problem that you hadn't considered. An OT assessment would rule out any physical issues like muscle weakness or dexterity problems. Waiting 2 years for a school assessment would put him ages behind if he has an issue. DD10 had similar symptoms with writing task avoidance, odd pencil grip, a mix of upper and lower case letters in writing, poor spacing of letters in words, slanting writing down the page, and just overall terrible penmanship. Her baseline printing was bad, but if she put a lot of effort into her work, she could make her writing legible. She was never failing any subjects in school. She was however, an excellent speller, but struggled getting her ideas down on paper. Verbally her vocabulary was amazing, but on paper her toughts lacked development and detail. Her OT assessment involved a Beery VMI, BTO2, and a ETCH-manuscript (for writing). The ETCH was important because it was timed and it showed that although DD10 could complete some of the writing tasks, it took her a considerable amount of time. The OT assessment found a fine motor skill delay, and some visual motor integration issues. She is now receiving OT therapy. Generally speaking, if it is a motor skill issue, kids aren't going to improve with time. They will continue to have delays acquiring new skills and fall further behind.
As polarbear said, all you lose is a little money if in fact your son falls within a normal range for fine motor skill development. Then you could focus more on processing/executive issues to see if you get improvement there. It sounds like he may have difficulty organizing his thoughts while writing.
