We investigated teachers' understanding of the Mathematical Practices (MPs; National Governors Association Center for Best Practices & the Council of Chief State School Officers, 2010) and the Mathematics Teachers Practices (MTPs; NCTM, 2014) using a Vignette Activity Sequence within a professional development setting with our Professional Development School (PDS) partners. Although results revealed misconceptions or incomplete understandings participants had about the MPs and MTPs, teachers made connections to their own practice. By highlighting how mathematics teachers at the middle and high school levels view the practices in relation to their classrooms, we were able to target areas to support high-quality teaching and learning of mathematics for future professional development with our PDS partners. This has important implications for mathematics instructional specialists, coaches, and professional development instructors working with teachers and their understanding of the MPs and MTPs.