<p>A lot of the time, people think they’re good at/like math until their first proof-based course (multivariable calculus or linear algebra, normally). Tests like USAMO (though I can’t see someone getting a score above 1 in that without having had precalc) and programs like the one you mentioned, though, tend to give you a decent sense, although competition math is again not the same as being good at math. Generally those who are good at math do get solid grades in lower level courses, but being ahead doesn’t necessarily show being good at math. In some ways, Geometry does show facility with math, since it’s the most proof-based of courses before the ones I mentioned, generally.</p>