Despite repeated findings that within-year growth in oral reading rate is nonlinear for many students, existing decision-making frameworks to evaluate response to intervention assume that growth is linear across an entire school year. The purpose of this study was to evaluate the consequences of failing to account for nonlinear growth among students in Grade 3 receiving supplemental interventions progress monitored with FastBridge Learning probes when using existing curriculum-based measurement of reading decision rules. Not accounting for nonlinear growth when using a goal line based upon expected growth between fall and spring assessment periods led to suboptimal outcomes for the data point, trend line, and median rules through 16 weeks of progress monitoring. Using a goal line based upon expected improvement between fall to winter benchmarks helped improved the accuracy of identifying cases that needed an instructional change (sensitivity) but led to lower levels of accuracy in identifying students that were benefitting from intervention (specificity). Using a gated framework in which growth was compared to both types of goal lines led to slight improvements in specificity among cases that showed nonlinear growth at the expense of sensitivity.