The present study outlines a specific three-level hierarchy of the cognitive system, in particular the relationship between cognitive and metacognitive processes in mathematics. The emphasis is on the impact of processing efficiency and working memory ability on the development of self-representation and mathematical performance. We developed and used instruments measuring pupils' self-representation, mathematical performance, working memory, and information processing and administered them to 126 pupils (8-11 years old) three times, with breaks of three to four months between testing. Results indicated that the development of each of the abilities was affected by the state of the others. In particular, processing efficiency had a coordinator role on the growth of mathematical performance, while self-image, as a specific dimension of self-representation, depended mainly on previous working memory ability. (Contains 5 figures and 2 tables.)