Criticisms

A wide range of conflicting criticisms have been leveled at the Montessori method. Some parents believe the Montessori environment leaves the children too free while others see the Montessori method as stifling to creativity. Some see Montessori schools as elitist prep schools for preschoolers while others question Montessori teaching priorities, and decry children spending time on such menial tasks as washing tables or arranging flowers. Some parents are put off by what they view to be Montessori teachers' unusual manners: some may appear too subdued, others too stern, none of them necessarily praising or teaching the children in a conventional manner.

The two primary critics of the Montessori Method in education theory are William Heard Kilpatrick and John Dewey. They thought that Montessori was too restrictive, and didn't adequately emphasize social interaction and development. Dewey believed that the Montessori Method stifled creativity.

Another criticism of Montessori schools is that they do not traditionally assign homework. The lessons taught in a Montessori classroom are not generally conducive to home use, and the materials are highly specialized. It would be unlikely that a parent would buy materials for this purpose. Critics allege that a child who transfers to a traditional school and is required to do homework will have trouble adjusting, although research has shown the opposite. Homework in some form has started to find its way into the Montessori curriculum, if in a somewhat forced manner.

For many years Montessori schools in North America did not believe in marking students according to letter grade system, and instead issued report cards that focused entirely on descriptions of the student's behavior and progress in class. Many parents complained that such report cards made it too difficult to get a clear picture on how well or poorly a student was doing in their subjects. As a result, some American Montessori schools now issue letter grades just as non-Montessori classes do.

Within the Montessori professional community, there have been squabbles ranging from minutiae to the core principles of the philosophy. Those from one training background may believe another is too strict or outdated while others are accused of diluting Montessori's scientifically derived vision of ideal environments to support human development.

Internal divisions regarding the classroom materials also exist. Some Montessori associations (such as AMI) are seen as adamantly opposed to the development or inclusion of new types of materials or ideas. A further problem lies in the traditional Montessori requirement that materials used in the classroom should be of natural materials (primarily wood) and of high quality. This creates a rift between well-funded schools who purchase material based on quality, and those schools who purchase cheaper materials (often plastic) in order to stretch their budget.

Dr. Angeline Stoll Lillard's 2005 book Montessori: The Science Behind the Genius (Oxford University Press) presents the first real comprehensive overview of research done on the comparison of Montessori educated children to those educated in a more traditional manner. Lillard cites research indicating that the children do better in later schooling than non-Montessori children in all subjects, and argues that more research is needed in this area.

A 2006 study concluded that Montessori students performed better than their standard public school counterparts:

On several dimensions, children at a public inner city Montessori school had superior outcomes relative to a sample of Montessori applicants who, because of a random lottery, attended other schools. By the end of kindergarten, the Montessori children performed better on standardized tests of reading and math, engaged in more positive interaction on the playground, and showed more advanced social cognition and executive control. They also showed more concern for fairness and justice. At the end of elementary school, Montessori children wrote more creative essays with more complex sentence structures, selected more positive responses to social dilemmas, and reported feeling more of a sense of community at their school.