Cudeck and Browne (1983) were among the first to discuss the advantages of taking a crossvalidation approach to testing of covariance structure models. The purpose of this paper is to expand on Cudeck and Browne's work in two directions. The first direction of expansion is into testing of latent class models. The second direction of expansion involves using crossvalidation to examine differences between groups, where groups may be formed by gender, ethnicity, region, etc. In the present article crossvalidation is used to help select models of early substance use onset in a sample of young adolescents. The results suggest that the nature of the substance use onset process and the rate of movement through the process are the same for males and females at seventh and eighth grade. However, the present study did find evidence for gender differences in substance use experience at the beginning of seventh grade, with males somewhat more advanced in the onset process. The results also suggest that double crossvalidation is greatly to be preferred over single crossvalidation.