We have tools to dynamically adjust curriculum difficulty
for students who value education, whether because they're self-motivated or because their parents make them. The challenge is what to do about the large number of students - at many schools the majority - who don't. When you where dynamically adjust to a student who doesn't particularly care to study, or doesn't have the support to do it properly, you end up with the recurrent scandals where a high school is found to be graduating people who can't read.
Extracurricular studies are always possible for the students who are furthest ahead of the curve, and good schools usually do accommodate that. For the rest, I would argue that a fixed number of tracks that insist on pulling students along is the only practical solution.
