Comment by dagw

My university had a proof based, let's construct the natural numbers from axioms and prove that a+b == b+a type course as the first class for aspiring math majors. It was a "weed out" course, not in the sense that it was particularly hard, but more in the sense of introducing students to this is what 'real' math is actually about, and not so much the stuff you were doing in high school. Some students decided each year that they didn't want to do 'real' math and went on to focus on other things.