B.H.
My daughter is having the same problem. She's in first grade. I think it's because she doesn't care. Not that she can't do it but it's just not important to her. She said last Friday in school she couldn't go to gym or something because she had to get "special help" with her writing. Her coloring use to be the same I knew she could do better she just didn't care and did fast work instead of quality work.
My daughter is very artistic and loves to draw, color you name it. Surprisingly she can print fancy letter, bubble letters she has the cutest creative handwriting and it's really good but she can't print standard letters very well at all. She keeps getting in trouble at school for not printing correctly on her papers and being to creative. I'll all about letting her be creative and sparking that imagination but realize she does have to do it the correct way too. When she did write a letter perfect I said "OMg that is the best letter "B" you've ever written wow" and when she got frustrated I told her practice practice practice it takes time to get good. We only concentrated on 2 letters last night also as to not overwhelm her. I'm not letting her know she's bad at handwriting or forcing it. We're just having fun and learning at the same time. Maybe have him concentrate on some letter's of a word he can relate with like the name of a favorite toy. If he's into football let that be the word of the night and practice the letter's in football work on other letter's another day.
So last night we took a one of those writing tablets and had fun with it. I would show her how to write the letter perfectly and then she would have to copy. It was alot of one on one attention so she ate it up. If she wrote really good then as a reward I would teach her how to do it in cursive or fancy. I took typography in college so have alot of ideas to share with her I guess. She had a blast. Although now she wants to jump to writing in cursive and still wants to abandon regular print.
I'm not making a big deal out of it. It'll come eventually and has no effect on anything else she does in school.
My brother is 26 and has the world's worst handwriting I've ever seen and can't write in cursive at all. It hasn't stopped him in life either.