Asklemmy

I have a question about rigid curriculums. This is mostly for high school. Many of my teachers had curriculums and syllabi that they had been using for years and kept them basically the same, and then there were the AP classes where the curriculum was determined by the AP exam. I felt that I learned really well in AP classes and we would get through much more advanced material in the AP classes than in others. And I also felt that the teachers who had developed somewhat fixed curriculums from experience taught much more efficiently than those who hadn't. It never felt like the teachers were changing their curriculum for each class whether it was an AP class or not because most had their curriculums kind of figured out over the course of teaching for many years. And most of the teachers I had in high school were excellent. So my question is, why is it believed that rigid curriculums don't work? Because in my schooling experience, whether the rigid curriculum was developed by the individual teacher or by an external organization (like AP), the class seemed to benefit from having fixed goals for the year.