When I meet new people and the topic of Montessori inevitably arises, there are a handful of misconceptions that are raised. One such misconception is that there are no computers in Montessori schools.
In general* what you may find is there are no computers in the 0-6 classrooms. The common Montessori consensus being that this is the time of the absorbent mind and is about building the child's senses, particularly through the hand-brain relationship. This correlates with what psychology and neuroscience have to say about child development and screen time for young brains.
In 6-12 (and possibly more 9-12 depending) computers are often found and used. In the schools I have been in and visited the viewpoint is that computers are a tool of our society, and that is what they are - a tool. The most ideal settings I have observed are where there are two - four computers in a classroom where each computer is designated for a particular purpose. For example, one for internet research, one or two for word processing, one for creating graphic designs/movies/multimedia or other relevant applications.
My personal view is that children need to learn how to use computers and smart devices safely, and learn to use them with purpose. I don't believe that requires them to come to school and sit in front of a screen all day. Unfortunately there are quite a few people (particularly parents, but also some educators) who feel if computers aren't front and centre in the classroom that children aren't learning.
Ultimately it is about making informed choices, considering all of the implications and keeping a balanced perspective. Parents. teachers and society as a whole need a respectful common ground for meaningful discussion rather than being polarized into a dynamic where constructive outcomes are hindered.
Here are some articles of interest relating to screens and brain development and/or physiological effects.
Grey Matters: Too Much Screen Times Damages The Brain
Screen Time Making Kids Moody, Crazy and Lazy
Screen Addiction Is Taking A Toll on Children
Technology and Kids: Startling Statistics Every Parent Should Know About Addiction to iPhone's and Screens
10 reasons Why Handheld Devices Should Be Banned for Children Under 12
And this article from Psychologist and author Sue Palmer Why The iPad is a Bigger Threat to Our Children than Anyone Realises
There is also this article about how here in Australia the Heavy Investment in School Computers Has Not Paid Off
* General being just that - there are always exceptions and each exception will have it's own reason.