Collaborating closely with a 10th-grade science teacher, we designed a Web-based learning environment (Web-LE) to improve student motivation to learn science. Factors believed to enhance intrinsic motivation (challenge, control, curiosity, and fantasy) were integrated into the instructional design of the Web-based learning tool. The Web-LE was implemented in the teacher's 10th-grade classroom as a three-day student-centered learning activity. Data collection methods included individual student interviews, teacher interviews, motivation questionnaires, and observations. This study revealed multiple forms of evidence that the Web-LE and the associated learning activity improved student motivation. This study illustrates the benefits of educational researchers working closely with teachers using design-based research methods to successfully solve instructional problems and identify reusable design principles. Design principles for the integration of intrinsic motivation factors into the development of similar Web-LEs are presented as well as directions for future research.