math is a subject that stacks abstraction on abstraction on abstraction, year after year. if a student didn't understand a fundamental math concept in an early

math is a subject that stacks abstraction on abstraction on abstraction, year after year. if a student didn't understand a fundamental math concept in an early year (perhaps for no fault of their own -- perhaps an undiagnosed issue impeding learning, or a teacher who didn't know the material well enough to teach it, or too many moves between too many classes and teachers), and the education system passed this student from math class to math class year after year without fixing the knowledge gap, so each year the student fails to absorb the year's new math concepts as they still haven't achieved fluency/mastery with the basics, then after some point it is no longer possible to compensate this with a brief remedial math course designed to plug a 1-3 year gap. maybe for some folks you'd need to bridge a 5-10 year gap in math education, which could be achieved with customised tutoring perhaps, for 5-10 years. but a remedial course trying to teach a batch of students at once needs to assume some basic level of ability as a pre-req.