Whereas studies of the past 10years have shown the executive functions (EFs) in adults to be differentiated into at least three principal components (working memory, inhibition, and flexibility), EF structure in children is far less well understood despite a large body of research on the subject. A study was undertaken to test different structural models of EFs through confirmatory factor analysis (CFA) on a large sample of typically developing kindergarteners (N =272). The method employed sought to remedy the shortcomings of past research in this field such as absence of CFA, insufficient number of EF components tested, insufficient number of indicators per latent variable, and absence of control on processing speed. Children were assessed using a battery of EF tasks developed by the researchers to measure working memory (WM), flexibility, and inhibition (backward word span, backward block span, fruit Stroop, day–night test, hand Stroop, Trails-P, card sort, face sort, and verbal fluency shift). CFA results show the best-fitting model to comprise two factors, namely, an inhibition factor and a WM–flexibility factor. Invariance analyses suggest that this structure is the same for girls and boys and that latent variable means do not differ by sex. These results support the hypothesis of EF differentiation during development. The researchers formulate other hypotheses regarding neurophysiological development.