I experienced this in math when I was in the 2nd to 8th grade until I was required to start taking college level math classes in 9th grade. The teachers notice the student talents through grading and recommends them to take a placement test. Placement tests are based on math/english/science - they see if student comprehends the work or either knows the patterns/logic behind each. If student does well, they assign more test. So for example when I was in the 2nd grade, they moved me up to 7th grade math and continued to move me up until I was forced to take college math online in school.
So yeah, they test out.
