Okay, MANY if not all, Kindergarten kids.... DO NOT WRITE WELL or neatly.
In time, as their fine motor skills develops, they will get better at it.
This is very COMMON.
Don't worry!
Also, boys tend to be messier at writing.
COMMON.
Don't worry!
Just have him, do coloring books, color inside the lines, and write for FUN.
I wouldn't worry.
Kids at this age, do NOT write all uniform and neat and perfect. NORMAL.
I have 2 kids, boy and girl. My son and most boys, per the Teacher, write less well..... and is VERY COMMON.
My son is now in 1st grade... and his writing has NATURALLY improved.
BUT his Teacher says, that kids this age, are not experts at it yet. Especially the boys.
DO NOT WORRY!
Really.
This is very very very, common.
Kids in Kindergarten... are NOT "mastered" at these things yet. Not at all. They are learning, it.
No kid, will be perfect. All kids need improvement in something. And penmanship is something that is very not-neat in Kindergarten.
MOSTLY don't "compare" him to others. Or he will get a hang up about it.
Take it with a grain of salt.
ALL throughout their school years, there will ALWAYS be something that a child "needs improvement" on. ALWAYS.
While we wish our child was "perfect" in all areas.... this is not normal.
And it can stress out a kid.
Just because a child needs "improvement" in an area, it does not mean they are doomed. It just means, they need improvement. ALL kids do.