My son has just started in a small starter British school in Germany at the beginning of year 2. Up till now, we have done Montessori education and home schooling for the past 5 months, since we moved here. His new school has asked us to suggest resources, books etc. that will help to keep him challenged, particularly in problem solving and maths, as he is so far beyond the other kids in this area. They are going to give him private math lessons, but the tutor is not terribly good at math, and would like further suggestions. Does anyone have any suggestions?