How many undergrads are actually  being taught by graduate students instead of professors either with or without tenure?

There are at least 1500 Graduate Teachers/Researchers at Duck U.  .

Their union is the Graduate Teaching  Fellows Federation.   Their last strike was in 2016, I believe.  


http://www.oregonlive.com/education/index.ssf/2016/07/university_of_oregon_reaches_a.html

 http://gtff3544.net/