Background: Although previous correlational studies have shown that both symbolic and non-symbolic abilities relate to mathematical abilities, correlational studies cannot show the cause and effect of these abilities for mathematical success. Aims: The current study examined the effect of a non-symbolic training program, called PLUS and a symbolic training program, called DIGIT, to provide further insight into the causal nature of domain specific factors that contribute to mathematical abilities. Methods: and Procedures: Forty-nine preschool children who had low mathematical abilities were recruited and randomly allocated to the DIGIT and PLUS training programs. Performance on a number of mathematical tasks was compared to 20 preschoolers with no mathematical difficulties. Outcomes and results: Performance in both training programs improved on the Test of Early Mathematical Abilities as well as on a non-symbolic Approximate Number Sense task, counting tasks, and digit recognition tasks, immediately after five weeks of training and this improvement remained six months later. Conclusions and implications: This study provides further evidence that symbolic and non-symbolic abilities bi-directionally impact on each other and that ordinality knowledge is an important factor of mathematical development. (author abstract)