MAEL has just issued a further volume in the series of instructional modules for the 6-12 primary curriculum. The book is titled Mathematics 3 and, as well as extending the maths coverage to KS2, it covers many topics which are more advanced than those in the UK National Curriculum (e.g. number bases and extracting square/cube roots). The rationale for this is that, if the Montessori curriculum has been correctly followed, and the children given time to practice new concepts/techniques until mastered, they will start to progress at a far more rapid rate than children who have just been instructed. These topics will greatly extend their understanding and provide challenge (but one which is achievable due to the use of wooden models.)
Further volumes are in the course of produxtion.