I think that if we wish to evaluate the Montessori method, we need to avoid cynical laziness on the one hand and utopian expectations on the other. Some things that came to mind while reading the article and the reactions to it:

- Not all Montessori schools are the same. Not all are accredited by a Montessori body.

- Children may benefit from varying methods, and Montessori seems capable of absorbing or accommodating them to by having the teacher adjust to each child's individual needs.

- Individual needs do highlight the oddness of modern education, of how impersonal and bizarrely artificial it is. In a natural setting, children grow up in a family in which they learn from their parents and siblings, through the interactions with friends, and so on. Our social interactions, especially those that take place in the family, are all about responding to each other's individual and particular needs. Learning and what is needed to learn falls under this category of human needs. Learning is fully integral and self-same with life itself, not some thing to be artificially set apart into some separated, alienated thing, a factory that thinks of students as units.

- As Montessori was Catholic, and Catholicism accepts the doctrine of original sin, it is more sensible to presume that she did not accept a Rousseauian anthropology. However, a rejection of Rousseauian anthropology doesn't automatically construe children as little monsters or reject the notion that we may become corrupted by others later in life. As a Catholic, Montessori would also be familiar with the age of reason before which children maintain innocence of any personal sin (sin entails culpability, culpability entails assent, assent entails understanding, and children still lack understanding). Of course, children can be said to be selfish in the sense that early in life, they have a good many basic needs that need to be met by others, etc. The effects of original sin concern the greater or lesser insubordination of both the corporeal faculties and the will to reason (the tendency to sin is a tendency to act, with greater or lesser awareness, against reason and what reason informs us is the good).

- I doubt the encyclical criticizing "scholastic innovators" was criticizing Montessori specifically or all educational reform. Papal encyclicals are not some kind of grumpy, curmudgeonly grunt of the pope in which he complains about things young people are doing that he doesn't like. They're often quite pithy and contain a good deal of foresight and depth (Pius X's predictions w.r.t. "modernism" have played out, for example). Note that at the time, the modern system of schooling was not that old (some say it was inspired by Prussian methods). What he was likely criticizing were strange fads in education rooted in really bogus philosophical anthropologies. All education systems make tacit assumptions about human nature, and if they are wrong, they will misshape educational methods and possible misshape the child. There is no way Montessori held the do-what-thou-wilt view of children or would have opposed punishment categorically. She may have only objected to the prevailing educational paradigm, and in it, the way punishment was used.