Using a framework of assessment literacy that included principles, tools, and purposes, this study explored the assessment literacy of 11 secondary preservice teachers. Participants' journals, teaching philosophies, and inquiry-based science units served as data sources. We examined how the preservice teachers understood assessment tools as well as their reasons for using assessment. Additionally, we investigated how the preservice teachers incorporated assessments into inquiry-based science units. Analysis of these documents indicated that preservice teachers recognize the need to align assessments with learning goals and instructional strategies and are using a variety of assessments. They understood several ways to use assessment for learning. However, the inclusion of assessments contained within the science units did not fully align with the views of assessment the preservice teachers presented in their teaching philosophies or journals. Instead of using a variety of assessments that reflect science reforms, the preservice teachers reverted to traditional forms of assessment in their science units. Teacher education programs need to place more emphasis on developing preservice teachers' assessment literacy so that they are better able to select and implement a variety of appropriate assessments to foster student learning.