I stumbled across this book and it has made a huge difference in how I positively reinforce my son.

Praising Boys Well-Elizabeth Hartley-Brewer

It states that boys and girls respond to praise differently and I have found that if I point out specifics in his handwriting he does a much better job.("I really see you care about your work here." Thank you for taking the time to put in an effort. It really shows. etc) instead of just "good job". "It looks really nice."

*Opinion alert*
I think boys pick up on the fact that girls love, love, love to be more creative with handwriting so they (boys) don't want to. I really don't mean to generalize here, I am just suggesting an opinion since there are a lot of threads on here about boys and handwriting. I also believe they are behind in motor coordination until age 9 (at least that is what I have read). laugh