Understanding the cognitive processes, skills and strategies that examinees use in testing is important for construct validity and score interpretability. Although response processes evidence has long been included as an important aspect of validity (i.e., "Standards for Educational and Psychological Tests," 1999), relevant studies are often lacking, especially in large scale educational and psychological testing. An important method for studying response processes involves explanatory mathematical modeling of item responses and item response times from variables that represent sources of cognitive complexity. For many item types, examinees may differ in strategies applied to responding to items. Mixture class item response theory models can identify latent classes of examinees with different processes, skills and strategies based on their pattern of item responses. This study will illustrate the use of response times in conjunction with explanatory item response theory models and mixture models, to provide information relevant to test validity and, hence, to score interpretations.