When I was in elementary school, we had different classes that were segregated by ability. We had different subjects with different teachers and different stude

When I was in elementary school, we had different classes that were segregated by ability. We had different subjects with different teachers and different students, and students were moved to different classes as their abilities changed. So if I were good at reading I could be in the more advanced reading class, but if I were bad at math I would be in the lower math class. If I improved at math I would be moved to a more challenging math class. Is this no longer the case? This was 3rd-6th grade, I don't remember much before those grades.