Mathematical reasoning is the ability of inductive and inferential reasoning with mathematical concepts that underlying cognitive variables play an important role in explaining it. The purpose of this study is to model the role of divided attention and working memory in mathematical reasoning with the mediation of mathematical knowledge and fluid intelligence in fourth grade elementary students. This study is non-experimental (descriptive) and a type of correlational study in which data were analyzed by Path Analysis. The statistical population of the research included all male fourth-graders of the primary schools in District 4 of Qom from which 213 students were randomly selected by two-stage cluster sampling. The study used different measures and instruments including the Integrated Visual and Auditory Continuous Performance Test-Second Edition (IVA-2 CPT) for measuring different types of attention, the Working Memory Index of the Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV), the Culture Fair Intelligence Test (CFIT), the knowing questions test and the mathematical reasoning questions test of TIMSS 2015. The findings of the study showed that all path coefficients are significant and appropriate model fit indices were obtained. The results indicate that working memory influenced by divided attention predicts mathematical reasoning with the mediation of mathematical knowledge and fluid intelligence. The research helps to develop in mathematics learning and cognitive rehabilitation of mathematical disorders by identifying the role of important cognitive variables in mathematical reasoning.