Teachers' assessment practices greatly influence student learning. However, the level of assessment literacy among teachers is inadequate relative to classroom assessment standards and expectations. Assessment literacy includes interpreting results of various assessments, creating assessments that are aligned to learning targets, using assessment results to understand students' gaps in learning, and adjusting instruction accordingly. This formative program evaluation used mixed methods to examine a professional learning program for teacher leaders in a public school district. Using Kirkpatrick's model, participants' reactions, knowledge and skill development, and changes in practice were evaluated to determine the effectiveness of professional learning and inform future professional learning for the district. Findings indicate that teachers enjoyed the professional learning and felt it was valuable to their practice. Participants proficiently identified the process of designing a robust classroom assessment system including developing, using, and analyzing classroom assessment and showed developing skills in identifying kinds of learning targets and defining reliability and validity. Teachers' approaches to classroom assessment did not change significantly, remaining teacher-centric and endorsing an Assessment for Learning approach before and after professional learning. Appreciative inquiry interviews with teachers revealed changes to classroom practice, confidence in using assessment to improve instruction, and the value of professional learning communities. Teachers conveyed the value of formative assessment in meeting the needs of all students and lowering students' affective filters. Results support the importance of the socio-cultural context in improving teachers' assessment literacy and provide a model for effective professional learning that improves classroom practices. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]