Hey, this doesn't sound too different from the adaptive diagnostic Maths Pathway (https://mathspathway.com/) has. It starts at Level 1 and retests all mathematical knowledge of the student until it reaches their zone of proximal development (ZPD). It's all within a classroom environment, but it means all the students are learning the maths that suit them, not a one-size-fits all which is the issue you are referring to I believe.

Full disclosure: i work at maths pathway.