I'm a Montessori teacher (19 years in the classroom) and I've never heard of this. If her rational is that the kids will "think" before writing, this is not sound. Children "think" with their hands and with movement. Montessori showed how writing comes before reading, not after. I would alter this slightly to say that they are mutually dependent. Montessori teachers want to encourage writing in any form. At this age the children learn from their mistakes. That's pretty much the point, and the reason why Montessori doesn't focus on evaluating or correcting. The children do that.
If this teacher had said she doesn't have erasers because the kids can see their progression, it would make sense to me. I still would allow erasers because some children get very upset if they can't rub out their errors!
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