How often do people change thier homework and other assignments when teachg the same class for multiple years/semesters?  This semester is the first time I've taught a class for the second time, and I've noticed there's a certain (small) fraction of students who are just copying last year's answer key on homework assignments.

So I've come to realize that my least favorite thing about teaching inorganic chemistry is grading their homework assignments.  I typically have about 15 students and in the past I have assigned weekly graded problem sets.  They are allowed to work together on the homework, but must hand in individual papers.  I get bogged down in the somewhat mindless repetitive task of grading their assignments.  That said, I do tend to try and challenge students through homework and it has typically been a reasonable chunk of their grade in this class (20%) which helps to balance the difficult exams.