Assessing student performance is one of the most critical aspects of the job of a classroom teacher; however, many teachers in the United States do not feel adequately prepared to assess their students' performance. These feelings of inadequacy are exemplified when placed against the context of the No Child Left Behind Act of 2001, especially with its increased focus on accountability and assessment. This study examined the effectiveness of a two-week classroom assessment workshop for inservice teachers. The workshop was based on the "Standards for Teacher Competence in the Educational Assessment of Students" and focused on discussion, practice, and practical application through performance assessment tasks. The study utilized a parallel mixed-methods design. Teachers were pre-tested and post-tested using the "Assessment Literacy Inventory." Additionally, teachers kept daily reflective journals in order to document their experiences. The training was shown to be highly effective for the teachers, as evidenced through the dramatic increase in post-test scores over pre-test scores, and perhaps even more so through critical examination of their reflective journals. (Contains 2 tables.)