Assessing student learning to adapt instruction to support learning is an important skill all teachers need to develop. However, it is not an easy task for teachers and even more difficult for new teachers. The current study aims to explore an alternatively certified new chemistry teacher?s understanding and practices of classroom assessment to help educators and researchers to support teachers? assessment literacies. This study used holistic case study design to explore the teacher?s assessment literacy. Pre/reflective interviews, observations, classroom artifacts, including assessment tasks and a survey, were used as data sources. The results suggest that, in theory, the teacher?s understanding of assessment aligned with current view of assessment as she mostly valued formative function of assessment while, in practice, the teacher faced difficulties to practice assessment as she preferred and did not select and use appropriate assessment tasks to accomplish her aims, such as supporting conceptual learning.