@PurpleTitan I guess St. Andrews is somewhere in between Oxbridge and US. Hers have 5 or 6 students. They are expected to actively participate and are graded on participation, ie if they hand you the dry erase marker you better be able to do a given problem on the board. They are typically one hour a week.
When I TAed chemistry at a UC there were 30-60 students in a discussion section and it was them asking me questions. Attendance was not mandatory and participation was not graded.