In my hometown in the 80's, elementary school kids were not allowed to use ballpoints. Fountain pens were allowed from the 3rd grade. Before that, wood-based pencils only. Even mechanical pencils were forbidden. It was said that ballpoints and mechanical pencils, especially the former, would have very negative effects on developing one's handwriting.
This was the case for Chinese, in which a good handwriting was highly regarded. As far as I know, there are no studies to prove or disprove the claim. It was true for me personally and for my classmates. I could execute many handwriting forms in pencils and in fountain pens easily while extremely hard, if ever possible, in ballpoints. After using ballpoints for a pretty long period, I couldn't write as well even if I picked up my fountain pens again. It had to take some time and some writing to get it back.