The main goal of this study was to analyze the contribution of predictors of both domain-general (working memory, processing speed, and receptive vocabulary) and domain-specific variable (estimation and magnitude comparison) processes to informal mathematical performance (numbering, comparison, calculation, and understanding of concepts) in preschoolers. In order to reach this, a structural equation modeling was used. A total of 158 preschool students (ages ranging from 52 to 64 months) participated in the investigation. Students were assessed with informal tasks measuring mathematical thinking, numerical estimation, symbolic and non-symbolic comparison making, coding, receptive vocabulary, and backward digit span. Results showed that domain-general (specially working memory) was the highest impact of the general-domain predictors on informal mathematical competencies and a limited specific-domain factor effects for magnitude comparison. The consequences for mathematics learning in initial school years are discussed.