Some of her theories are timeless, but some of her examples are not. She spends a lot of time equating schools with prisons, and I have to remind myself to remember the age she went to school in. That while are education system needs improvement still; there have been many improvements. One of them being many women can go on to higher education.
Montessori argues for the scientific, so I think that many who espouse her methods don't always look at the underlying reasons. There has to be science behind it. It can't all be what Montessorians have been classified as "hippie school." I think, based on readings, that she would have been horrified. Yes, students need to progress at their own pace, that they need space and time to do their work, but it is not a free for all. That there are limits and guidelines to it all. That there is science behind it, or there should be.