- To evaluate student learning in a computer-supported environment known as GenScope(tm), we developed a system for assessing students' reasoning proficiency in introductory genetics. A critical aspect of the development effort concerned the validity of this assessment system. We used a variety of methods to address traditional evidential validity concerns as well as more contemporary concerns with consequential and systemic validity. Specifically, we examined whether or not our assessment system helped students develop the understanding it was designed to assess. Our inquiry revealed strong evidential validity but only limited consequential validity. In response, we developed a set of formative assessments designed to scaffold student assessment performance without compromising the evidential validity of the assessment system. In addition to documenting and enhancing the validity of the system, these efforts demonstrate the utility of newer interpretive models of validity inquiry and the value of Rasch measurement tools for conducting such inquiry.