It has been presumed that children who reverse letters or words see them backward.  This is false.  They have directional confusion.  In the real world, the direction has no meaning.  For example, a chair is a chair no matter which way it is placed.  Changing direction does not change interpretation.  In the world of language, direction changes meaning.  Connect the bottom of a chair and it looks like a "b".  Turn it 180 degrees it becomes a "d", flip it upside down and it becomes a "q", and flip it again it becomes a "p".  Thus, direction changes the meaning.  The difference between "was" and "saw" is direction.