A large research gap exists between psychological research about intelligence on the one hand and educational research about competence on the other hand. Both constructs are only rarely examined within one study. From an educational psychology point of view and for construct validation of competence tests, this is necessary though to gain more insight into the relation of the domain-specific constructs. The present article examined the relation between two domain-specific facets of preschool teachers’ competence, mathematical content knowledge (MCK) and mathematics pedagogical content knowledge (MPCK), to intelligence by hypothesizing a nested-factor model. Three hundred and fifty-three preservice preschool teachers were tested on their MCK and MPCK and took the screening version of I‑S‑T 2000 R covering verbal, numerical, and figural intelligence. The data revealed, as expected, a strong impact of intelligence on the ability to solve the domain-specific test items. Nevertheless, MCK and MPCK had a significant additional impact on this ability. The initially strong relation of the two domain-specific constructs could fully be explained by the higher-order g factor which supported construct validity of the assessments furthermore. The discussion focusses on implications for measurement issues and future research besides practical suggestions.