In fact what they did was quite simple. The students were placed into three groups; advanced, average and slower learners. Notice, I didn't use a derogatory term. We're not talking about dummies or trouble-makers. What they managed to do was to let each group learn at their own speed. Too often the liberal thinker mandates that everything is equal for all. What they then fail to consider is their equality is holding back all these groups. The 'fast' kids are held back because the process they are subjected to is too slow for them. Slower learning kids continue to fail because they can't keep up with the faster kids.
The 'equalitarians' fall into their own trap. Being equal across the board doesn't raise the level of everyone, it often does the opposite, dragging all performances down. They succeeded by letting the faster students learn at their own rate thus succeeding. The slower learning succeeded by, guess what, doing the same thing, learning at their own rate and thus succeeding. Grouping by ability doesn't need to have a stigma as the opponents claim, it raises their success rate by giving them the chance to succeed, thus negating any stigma by having a positive outcome.
It's not about the end justifies the means, it's about doing something that works.