Continuous assessment and GPA in the American system, which means not just finals/final papers at the end of the semester but also midterm tests, quizzes, papers (written essays, not tests), labs, some times class discussion in seminar classes all factor in to your grade, and they are averaged in to a GPA (so everything counts from when you start undergrad). Differs from Oxford where the marks you graduate with essentially all come down to big tests at the end of your last year.
Probably more opportunity to do research as an undergrad in ND though @collegemom3717 can chime in on those opportunities at Oxford these days.