My son was doing long division in Montessori K as well but he still had a bad year there. DS7 was a happy child in his play based PreK the year before but in Montessori he was miserable, acted out at home, and wanted to be homeschooled. His perfectionism got out of control during the first few months there. I had an extremely unpleasant conversation with one of the teachers which finally prompted us to get him tested.
Our younger one (3 at that time) got to spend one year in the very same Montessori classroom where he had to count the dots again and again because he wasn't able to write the numbers yet. The teacher herself told me that they wouldn't move him to a different material till he learned to write numbers, but not to worry since none of the 3 year olds could write. It was a disaster for him, he refused to go there on countless occasions.
Next year he went to the play based PreK and was happy there. The teacher let him read to the entire class. She let him do as much or as little as he wanted. They might have not taught him anything new but they didn't make him repeat boring tasks over and over.
Trust me, long division in K isn't everything. That said I am glad I didn't have to teach it to DS7
