In a traditional Montessori School, 3,4,5 and 6 year old ALL work on what they find to be stimulating. In our Montessori 3-6 class there were 3 year old putting together the 100 board and manipulating it to make Math Sentances and Kindergarteners still working with a friend to fill it in. There were puzzles of the world with LOTS of pieces. Children were given opportunities to write books and could make the book as advanced as they like. They however were NOT allowed to waste paper. They had to learn to be responsible learners.
There was a reading loft in my kids' class. They could read whatever they wanted up there.
There is no set place for you child to be any any particular time, so there would be no reason to hold him/her back. As with any classroom, there may be a need to provide harder books or harder puzles...and even grade skips. But the Montessori way of learning shouldn't be thrown out just because a child is advanced. The school we were in was more than happy to skip a child if that child was ready.
The Montessori way of teaching was actually invented to teach mentally challenged children to care for themselves.
