Generalizability considerations are widely discussed and a core foundation for understanding when and why treatment effects will replicate across sample demographics. However, guidelines on assessing and reporting generalizability-related factors differ across fields and are inconsistently applied. This paper synthesizes obstacles and best practices to apply recent work on measurement and sample diversity. We present a brief history of how knowledge in psychology has been constructed, with implications for who has been historically prioritized in research. We then review how generalizability remains a contemporary threat to neuropsychological assessment and outline best practices for researchers and clinical neuropsychologists. In doing so, we provide concrete tools to evaluate whether a given assessment is generalizable across populations and assist researchers in effectively testing and reporting treatment differences across sample demographics.