Firstly I personally don't believe this for a moment but have been surprised to see how it appears to be prized ahead of other attributes by primary teachers. (Am sure not all primary teachers but there appear to be some).
Handwriting matures at it's own rate surely? It needs teaching to acquire fluidity but if a child doesn't 'get it' relatively quickly why is this often seen in such negative light?
I appreciate poor handwriting might hold children back but there appears to be this ingrained attitude with some teachers?
I have had reports for one of mine that say 'handwriting is still well below the standard we would now expect'..and so on.