This study is an evaluation on whether middle‐level mathematics teachers' participation in a week‐long in‐service course on middle‐level mathematics concepts increases their understanding of this content. A secondary purpose of this study is an exploration of teacher perceptions before and after the institute via self‐report surveys. Participants include 31 middle‐level mathematics teachers who attended at least one of the two in‐services, one emphasizing algebra concepts and the other emphasizing probability and geometry concepts. The findings indicate that teachers' content knowledge significantly improved, as measured by pretest and post‐test results. The self‐report survey responses did not change as a result of participation in the in‐service, but overall patterns of responses in both the quantitative and qualitative survey data indicate how the institutes can contribute to a larger professional development strategy. Both in‐service courses are described and implications are discussed.