TBH, Montessori is designed to start from birth (obviously NOT in a school environment!!
) Maria Montessori did lots of research about something called the "external pregnancy" - something I imagine most mamas on this site actually take for granted and do anyway. It is all about allowing the child to take the lead, no pacifiers, extended breastfeeding, sleeping with the child, but when the child (if the child) is in their own room, allowing them to sleep on a mattress rather than a crib so they can get up when they need to. Keeping "attractions" in their bedroom to a minimum, but enough to entertain them. Encouraging the child to mimick the things that are done around the home, ie: baking, sweeping, polishing, feeding the cat, that kind of thing that fosters independence etc.
This is a highly crude and brief description!! I apologise.
We are lucky enough were we are to have a toddler program within our Montessori school and I liase with the toddler teacher, as I am a childbirth educator, to encompass some of these premises within my parenting education. They start as young as 15 months, which, if used as the way it is intended as an extension of what happens at home anyway, should be some nice "social" time and hopefully a gradual wean to the first year of primary (aged 3). I am not entirely sure that I am comfortable with children leaving their mamas at 15 months and that is another story, however, my daughter is going to start this week, she is now 2. I will surely be slated by some, but for her, I think it will work. She has two older brothers who have been at Montessori for a while now and so she is very very familiar with the school and her orientation has gone really well. If she were at all uncomfortable about being left or showed any signs, I would review it, and, like all of us on here I guess, her school time will by no means be an abandonment, but one where there is 100% commitment by me and my husband, liasing and interaction with the staff.
So, a long winded POV - !!