We have often seen how slow learners suddenly click and quickly come from behind and pass everyone to go far ahead. Here is a real life record of a teacher using the resources at Khan Academy to make it happen. See it from between 9 to 14 minutes.
Today these sort of positive surprises come about randomly. If you are unlucky you missed the opportunity or even serially missed most of them. We now have the technology to make new approaches possible. Think mass customization.