The present study, using a sample of 1,491 grade 10 students from a mid-western province in Canada, examined the validity evidence on the Canadian Tests of Basic Skills. Factor analysis of the 34 micro-skills (content by skill/process classification of items) of the four tests indicated that the Reading Comprehension, Written Expression, and Using Sources of Information micro-skills defined one factor and the Mathematics test defined another. The reliability evidence of this sample was reasonably comparable to the standardization sample. Sex-specific differences in mathematics micro-skills suggest clear targets for instructional mediation and future research. Differential prediction of mathematics cognitive skills confirmed uniqueness of mathematical processes. (Eight tables give analysis results.) (Author)