This paper describes the Assessment Practices Framework and how I used it to study a high school Chemistry teacher as she designed, implemented, and learned from a chemistry lab report. The framework consists of exploring three teacher-centered components of classroom assessment (assessment beliefs, practices, and reflection) and analyzing components with the assessment triangle model (Pellegrino et al. in, "Knowing what students know: The science and design of educational assessment." National Academy Press, Washington DC, 2001). Employing the framework, I report the teacher's assessment practices, report the alignment in her assessment practices through the three vertices of the assessment triangle (cognition, observation, and interpretation), and suggest relations between her beliefs and practices. I conclude by discussing the contribution and limitations of the Assessment Practices Framework while conducting future research and supporting science teachers in assessing student learning.