I think you're painting it in an overly positive picture, because in theory it should work that way but in practice too many students are sent to the highest ti

I think you're painting it in an overly positive picture, because in theory it should work that way but in practice too many students are sent to the highest tier because of parental/societal pressure, even if not technically on the same level (so they're holding back the other), and on the other end the lowest tier is so riddled with kids that have bigger problems than lack of good grades so if you end up there it's also a problem. Also I'm actually not sure I wouldn't have preferred to have a wider range of people in the school, especially because I also saw problems with wide gaps in progression in normal class. Not an expert but I'd hazard a guess that for every main subject out of 30 people you could have easily moved 10 up one class and 10 down one class and then the result wouldn't have been worse than repeating the same things 10 times, per subject, and not to the same people.. (Spoiler alert: I hated school, I wasn't a really good student, my main motivation for staying and not slacking off completely was that I needed to graduate in order to be able to study CS, but I would have loved to focus on some subjects and ignore others)