I just think that any method of education is a series of tradeoffs. Time management and difficulty working on thing you don't like (and a lot of this is personal experience, both my own and in discussions with others) seems to be the largest tradeoff.

Bottom line is that almost no system gets implemented perfectly, so it's important to understand the common "failure" points. This seems to be the Montessori one.

Thats not to say this is a bad thing! Depending on your beliefs, decreased study skills and/or mediocre time management are way less important than maintaining a natural curiosity. But the skills some kids end up missing are very important in traditional schooling environments like universities and high schools.

it's not about the claim. we can't afford it not to. at least not for a system that we would like to apply nationwide (which is what i would like to do with montessori) because we don't always have the luxury of multiple schools in one region where kids can switch. maybe not even the luxury of multiple streams in one school, esp. in rural areas where there barely enough students for a single class. (at least by putting multiple years into one class, you need less students from each age group to fill a class, which makes smaller schools possible)

as a specialized school, not being able to handle very kind of student is fine. as a general school that would be a problem.

Time management and difficulty working on thing you don't like

what bothers me is that montessori is supposed to teach exactly that because you have more freedom to manage you time. so i can't accept that this is montessori's failure point. because it should not be. this is to vital a skill to miss out on. i don't know the answer for this. i am not nearly familiar enough with how he montessori method is supposed to work here.