Did you know that you can find Maria's Books Online, free to download?
The Montessori Elementary Material was reprinted and re-titled to Volume II of The Advanced
Montessori Method. This book can be downloaded here: http://www.archive.org/details/montessorielemen027888mbp This book written by Maria Montessori contains information on teaching Grammar, Math and Geometry.
I did a search on Montessori on this archive site and found 64 founds written by Maria or about the Montessori method.