The aim of this work is to analyze the dimensional structure of the Spanish version of the School and College Ability Test, employed in the process for the identification of students with high intellectual abilities. This test measures verbal and mathematical (or quantitative) abilities at three levels of difficulty: elementary (3rd, 4th, and 5th years in Primary school), intermediate (6th year in Primary school plus the 1st and 2nd years of Compulsory Secondary School or ESO), and advanced (3rd and 4th years of ESO plus the 1st and 2nd years of "bachillerato"--equivalent to High school). For each level there are two forms, X and Y. The research was undertaken with the results obtained from the application carried out for the validation and norming of the Spanish version of the test, and for which a representative sample of students from Navarre at these mentioned levels was taken. This study assessed the possible unidimensionality of the simplicity or the complexity of the structure of this test as an essential aspect of construct validity. To this end, the results were triangulated for the classic factorial techniques and non-parametric methods based on the item response theory. (Contains 10 tables and 2 figures.)