This study introduced and demonstrated a new methodology for item and test bias studies: moderated differential item functioning (DIF). This technique expands the DIF methodology to incorporate contextual and sociological variables as moderating effects of the DIF. The study explored differential domain functioning (DDF), so that the focus of interpretation for this test is on the "domain" rather than the item. This moderated DDF effect was shown in a multiple choice and constructed response provincial assessment that was designed to match a specific mathematics curriculum. Participants were 45,728 fourth graders, 45,022 seventh graders, and 43,525 tenth graders in British Columbia, Canada. Data were narrowed to create four contrast groups of communities that reflect differences in contextual variables: rural low-income, rural affluent, urban low-income, and urban affluent. Gender DDF was explored using a general liner statistical model. After statistically matching males and females on their mathematical ability, gender DDF was moderated by the contextual variables. Thus, this "moderation" approach allowed the investigation of sociological, community-based contextual variables that may help explain the complex functioning of DIF in large scale testing. The paper advocates a more "sociological" and "ecological" approach to help explain differences in item and test performance. (Contains 22 references.) (Author/SLD)