If you have 1 to 8, 9 kind of takes care of itself and becomes redundant anyway, As for 10, I take it you mean streaming by ability within subject? Not all kids are equally good at the same thing, some are good at maths, some are crap at it but really good at art. Mixing the kids randomly you end up with more capable ones getting bored and not paying attention, the less capable ones not being able to keep up and not paying attention either. How would you handle that? There's a case for saying that adequate resources should be available to give everyone the best education they can get but that's not the same as pretending everyone is equally capable.