The basic goal should be to allow ANY student to learn as much as he/she is capable of learning, at the time that is best for the student; and, if that results in some students or groups learning more than others, that’s not a problem. Everyone would benefit from this, and people nowadays are not prone to look down on slow learners. This is far from what we have now.
A few more thoughts:
1. There should be lots of alternatives, and no shame, for the slow learners.
2. Focus on motivation. Reject any approach that presumes that learning is something is poured into an unmotivated student’s head by the big spenders, rather that grabbed-onto by the motivated student.