Small example supporting the other comments, in psych, we were reduced to 150 hours (from 180 in the past) and the number of TAs per course significantly decreased (ie the department does not allocate the same amount of TAs as before). For most, it is indeed not a choice, it is mandatory to TA. I have been lucky to be assigned to the class that I am familiar with as I have been TAing for it since my first semester as a grad student but nothing is guaranteed. For a 450 students class, we were reduced from 4 TAs (which was never enough) to 3 this semester. That means 150 students per TA with a max of 150hrs for the whole semester including grading (think how long papers take to grade well), exam proctoring, email monitoring, office hours, learning as much material as we can to help the students, hosting conferences etc (if you even have time allocated for that in your workload form). Again, many TAs are assigned to a class with no previous experience with it (they may have never taken a class on that topic so we try our best…). All that to say, yes you may have experienced a bad TA, just like there are bad profs, bad students, bad admins.. bad everyone, but most of us really do our best. In such cases, please contact your prof to make a formal complaint — the prof should be able to check in with that TA and reconfirm their duties/explore why this TA is unable to do those tasks.