I was fired from a teaching assistant position when I was a grad student at Northwestern because I graded papers written in a statistics class on both content and English writing skills (grammar, spelling, punctuation and overall ease of understanding their data and models).  These students were paying around $17k/year back then.  I can only imagine what it costs now.  But they were not getting their money's worth - their writing skills were terrible.  I was dumbfounded at the time.  I get it now.