This article provides a description of a novel, attitude-focused, professional development intervention, and presents the results of an experimental pretest-posttest control group study investigating the effects of this intervention on primary teachers' personal attitudes toward science, attitudes toward teaching science, and their science teaching behavior. The training course integrated an explicit focus on attitudes towards (teaching) science with an inquiry-based learning approach and refrained from recipe-like, pre-structured, and content-based instruction examples. Results show that the training course had profound positive effects on primary teachers' professional attitude towards teaching science. Teachers improved in self-efficacy beliefs regarding science teaching, felt less dependent on context factors, and enjoyed science teaching more. In addition, the training course had positive effects on teachers' personal attitude towards science, including improved self-efficacy and relevance beliefs, and decreased anxiety. Furthermore, there was a large effect on teachers' science teaching behavior in the classroom and on the number of science related activities they engaged in during their personal lives. These results show that an attitude-focused approach is more effective in changing teachers' attitudes and science teaching behavior compared to merely being engaged in science teaching.