students use of relational thinking to solve number sentences is evident in all three countries by the end of elementary school. The extent of its acquisition varies between countries and between school. Even where it appears to be strong, there are still many students who seem unable to use it. Those who were consistent relational thinkers on number sentences were more likely to deal successfully with a sentence involving literal symbols and number terms than those who showed only arithmetical thinking on the number sentences.In all the three countries, particularly in Year 5 and 6, the majority of this latter group were unable to deal successfully with the sentence involving literal symbols. This group should be a special concern for teachers. They may obtain perfectly correct answers to number question through careful use of computational based approaches, but these approaches are clearly deficient when students are confronted with question using literal symbol where computation will not work.