This Educational Position Paper focuses on the design of a classroom-based reading assessment system for Wilmington Montessori School that provides: (1) evidence of children's progress across the developmental milestones of reading, (2) proactive information about children at risk of later reading difficulties, (3) a framework for teachers to monitor children's progress against the developmental milestones of reading (4) for the collection of information across the school community to evaluate the overall success of the school in supporting children's reading growth, and 5) for the school to hold to the principles of the child-centered Montessori philosophy. Teachers use many forms of formal and informal classroom-based reading assessments, and effective reading teachers use such assessments in an ongoing formative manner to inform daily instruction. Teachers' beliefs about assessment influence their use and interpretation of classroom-based assessments and are often counter to recommended best practices. A survey of teachers at Wilmington Montessori School indicates that while teachers have an interest in learning more about classroom based-reading assessment, they are unsure about the use of such assessments in a Montessori classroom, even though the Montessori Method supports the concept of the use of classroom-based reading assessment in the child-centered Montessori Classroom. A school-wide classroom-based reading assessment plan provides a framework for observing and collecting information to document children's growth as readers. Further, a school-wide reading assessment plan reflects clearly agreed upon goals for literacy, a common set of classroom-based assessment tools to track children's progress towards these goals, and a collaborative school environment supporting professional growth. The developmental stages of reading and the New Standards for Reading and Writing (1999) provide a framework for common goals for reading at Wilmington Montessori School. Tools for screening, progress monitoring, diagnosis, and program evaluation are proposed for Wilmington Montessori School. Recommendations are made for the specific use of assessments from preschool through the upper elementary years and for professional opportunities for teachers to develop their skills in using and interpreting reading assessments.