This study outlines a formative assessment system using a consistent set of cut scores on Curriculum-Based Measurement-Reading (CBM-R) probes and investigates four statistical methods for establishing cut scores. Cut scores were established using the Minnesota statewide achievement test in reading at grade 3 as the criterion for a successful outcome. Participants were 2,191 students from five districts in rural and outer-ring suburban east central Minnesota, each of whom completed the statewide achievement test in reading and also CBM-R probes between grade 1 and grade 3. This study examined the relationship between CBM-R and the state test and compared the utility and accuracy of each of four statistical methods for establishing cut scores. Receiver Operating Characteristic (ROC) curve analysis provided the most flexibility in establishing desired levels of diagnostic accuracy (i.e., sensitivity, specificity, positive predictive power, and negative predictive power). The benefits of a set of consistent cut scores for use within a response to intervention (RTI) framework are discussed. (Contains 5 tables and 7 tables.)