Reassessing aptitude: Introduction to a special issue in Honor of Richard E. Snow

Richard Snow's research influenced many students and colleagues, both directly through his findings and indirectly by inspiring others to carry on the work. A cross-section of his influence is represented in the articles presented in this special issue. Snow was guided by a respect for empirical, quantitative approaches, applications, and a concern for large issues. We present several themes in his work, including the importance of multivariate considerations of individual differences, adapting instruction to individual learners, a process understanding of aptitude, and an enlarged role for spatial ability.