The goal of the User-Centered Digital Library Project, conducted by the National Center for Accessible Media (NCAM) at WGBH, was to adapt the Teachers' Domain online digital library to enable teachers and students with disabilities to more readily use the resources in science classrooms. NCAM added accessibility features such as captions and audio descriptions to existing resources, tagged the resources to indicate which accessibility features they have, created an advanced search function that allows users to search for resources with particular accessibility features, and developed an accessibility portal that orients users to the adapted site. The EDC/Center for Children and Technology served as the external evaluator for the User-Centered Digital Library Project. The goal of the evaluation was to inform project activities and to document the impact of the adapted version of the digital library on teachers and students with disabilities. In Years 3 and 4 of the project, the evaluators conducted user testing with teachers and students with hearing, vision, and multiple disabilities including mobility impairments, to explore the potential impact that the adapted Teachers' Domain site may have on teachers and students with hearing, vision, mobility impairments and other disabilities. To better understand how the adaptations made on the Teachers' Domain impact users, they compared the use of and outcomes for the adapted site to those for the original site. They found a number of important differences: (1) Teachers' Lesson Planning; (2) Teachers' Classroom Use; (3) Students' Responses to the Teachers' Domain Resources; and (4) Student Learning and Understanding of Science Content. This study provides initial evidence of the potential impact of the adapted Teachers' Domain site on teachers' lesson planning, classroom practices, and student learning. Given its limited scope, it was not designed to investigate causal claims about the effects of the adapted site. However, the findings reported here are consistent with such causal connections and suggest hypotheses that could be explored in larger-scale experimental studies. (Contains 3 figures, 12 tables, and 1 footnote.)