A teacher's sense of self-efficacy has been consistently recognized as an important attribute of effective teaching and has been positively correlated to teacher and student outcomes. A number of studies show the impact of teachers with high levels of efficacy. Students of these teachers have outperformed students who had teachers with lower levels of efficacy on the mathematics section of the Iowa Test of Basic Skills. Greater achievement was also found in rural, urban, majority Black, and majority White schools for students who had teachers with high levels of self-efficacy. In addition, studies have shown that teachers with high levels of efficacy have demonstrated different characteristics related to work ethic and pedagogical practice than teachers with low levels of self-efficacy. The benefits of having high levels of efficacy have been firmly established; therefore, many researchers have explored methods of increasing levels of efficacy in preservice teachers; but few studies have explored the concept of raising inservice teachers' efficacy levels. This is partly due to the fact that the concept of self-efficacy, as developed by Bandura (1993), has been thought to impact novice individuals early in the context of new learning, thus limiting the studies of practicing or in-service teachers. In this article, the authors examine teachers' self-efficacy and change over time. They detail self-efficacy and the ways that self-efficacy can impact teaching. In considering the context of an inservice teacher with lower levels of specific content knowledge, the authors posit that content courses which are designed to support a teacher's development of content knowledge and pedagogy can be a valuable way to increase levels of self-efficacy. This study investigates whether inservice teachers' levels of personal efficacy and/or outcome efficacy changed as a result of completing courses in mathematics and/or science that intertwined content acquisition with pedagogy. In addition, the authors are interested in the reasons teachers participated in content courses and if this information helped identify characteristics of teachers with high levels of efficacy. (Contains 7 tables.)