Antonia Forest fans

This is just a guess, though I may have heard something, but if all the children are sitting in one long row, fairly close together, if someone in the middle is writing with their left hand they would interfere with their neighbour on their left. Plus a general thing that everyone had to be the same -no individual writing styles allowed, they all had to use the same script. And the whole left handed thing has ancient origins- left and sinister have the same meaning.