I wish teachers would get it

Youngest came home yesterday with her little weekly folder of graded papers. She had scored a 100 on one of her math assignments and the teacher took off 4 points for not showing her work.  Ugh..,so frustrating, if the kid can do the problem in there head (and correctly) who cares if they don’t show their work. Yes, I know that not everyone can do it in their head but why force kids who don’t need it to use strategies that are just a time filler for them? Instead of docking points because the work is too easy for her, why can’t you challenge her with different levels of problems?  Ok end of rant.