In a mixed method study the usability of SESAM was examined. SESAM is a server which gives teachers access to media for their lessons. SESAM offers digital videos, digital pictures, texts, software and hypermedia for teachers and pre-service teachers. To explore the ease of use of SESAM by teachers we developed a ten-minute test setting. A first browsing process of the teachers was videotaped and to get insight in their cognitions the think aloud method was used. The data collection and analysis was carried out using Morae a professional usability software. The data was analyzed with qualitative methods. In addition different questionnaires were used to collect data about the computer competency of the teachers and their evaluation of the website. The ten minute tests were carried out with 49 teachers and pre-service teachers and led to several recommendations which caused a relaunch of the website. During the second phase the qualitative and quantitative data collection were repeated with 53 teachers and pre-service teachers to evaluate the success of the relaunch. Participants with less media competency profited especially from the relaunch, with the benefits being statistically significant.