Summary.A major source of empirical support for the generally accepted common factor structure of intelligence is (exploratory) factor analysis. This excludes the possibility of many alternative models which can only be evaluated through the confirmatory methods of structural modelling. Using this approach in the analysis of Richmond Basic Skills Test data, we demonstrate that a different kind of model where one type of ability leads to and influences another (a simplex) not only fits the data, but is also consistent with theory in developmental psychology. An elaboration of the simplex, termed for convenience a ‘split simplex’, enables all the tests (verbal and mathematical) to be incorporated in one model. We conclude that the simplex and its variant should be considered as plausible alternatives to the classical mo