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<p>Why do you write as if this were unusual or contradictory? Why would it be unusual for one high school student to take calculus in high school, then attend a university and be placed in a more advanced math course and do well in that, while another student in the same high school goes on to the same university but needs to take remedial math courses? Or even for the same student to be advanced in math but remedial in English, or vice-versa?</p>
<p>At any school transition (high school -> college, middle school -> high school, elementary school -> middle school), there will be some advanced students at the top grade of the lower school ready for course work at the bottom grade of the higher school in some subjects, and other students at the bottom grade of the higher school who need remedial work for things that they should or could have learned in the lower school. Some students may be advanced in some subjects but behind in others, so eliminating social promotion and having stricter graduation requirements for each transition would not be a complete solution.</p>