A number of Montessori schools--AMS and AMI--have started 18 mom-2 yr 9 mo programs for a few reasons. There are Montessori principles that can be taught at this age--all of them practical skills. Maria Montessori did not design any materials for this age group, as she believed that these younger children would be wholly engaged in imitation of the parents and exploration of their world. At dss' new school the 18 mo-2 yr 9 mo classroom has no "Montessori" materials--it's all tiny brooms, pouring bowls, spoons and beans (to learn to balance, empty and fill) and so on. They help the toddlers potty train as well. It's also a program, frankly, because there's a demand for it from parents who don't want to feel like they're just sending their little ones to day care--they want to feel like it's something more than that.
It also provides a "feeder" system for the older age groups. And it's another source of income, though toddler programs don't generate much $ because the student
cher ratio, at least here in MA, must be 11:3, whereas at the 2 yr 9 mo+ ages it can be 10:1.
I'm here in Amherst, MA, and the school my dss' will go to has a directress whom I find to be quite direct. I asked her about nursing toddlers in the program, and whether that was an issue, and she looked surprised and said, "Of course not. They're still little. Plenty of parents nurse at that age." She went on to say, however, that past 3 or 4 it could be an issue for some kids trying to assert their independence--but she was very careful to say that it's a case-by-case situation.
Michael Odent, a well-known Montessori "expert" (sarcasm) has written a lot about weaning at 9 months, never nursing to sleep, teaching babies sleep independence. I don't believe any of it. I pick and choose, just as I pick and choose from Sears' statements.
I think your son's teacher made it clear how she felt about him, and I'm so sad that someone working with small children could be so cold. Good luck searching for the right fit for him. I know how hard it is to see your wonderful child not be appreciated--after our bad experience we think we've found a good place with good teachers.