I'm left-handed and always tilt paper at least 45° clockwise, effectively writing from below. Never had any smudging issues, even with fountain pens, as my hand simply never goes over any ink. Left-handed people who write from above by bending their wrist have always confused me, as it's both less comfortable and does not completely avoid smudges.

You meant counterclockwise, I guess? Because clockwise would mean to write from above, not below?

Interested because my son is learning to write and is the only leftie in the family, so I struggle to help him.

You had me triple check but it's definitely clockwise, i.e. the top of the sheet is actually facing top-right from my perspective:

           ______________
          /              /
         / Hello        /
        /     /|       /
       /    __/       /
      /    (  )      /
     /     / /      /
    /    /   /     /
   /    /   /     /
  /____/   /_____/
      /   /

The arrow below the o of hello being the pen, and the thing below being my left hand and arm (I actually have fingers IRL, ASCII art is difficult)

Counterclockwise, correct.