Curriculum-based measurement of oral reading (CBM-R) is frequently used to set student goals and monitor student progress. This study examined the quality of growth estimates derived from CBM-R progress monitoring data. The authors used a linear mixed effects regression (LMER) model to simulate progress monitoring data for multiple levels of progress monitoring duration (i.e., 6, 8, 10...20 weeks) and data set quality, which was operationalized as residual/ error in the model ([sigma][subscript epsilon] = 5, 10, 15, and 20). The number of data points, quality of data, and method used to estimate growth all influenced the reliability and precision of estimated growth rates. Results indicated that progress monitoring outcomes are sufficient to guide educational decisions if (a) ordinary least-squares regression is used to derive trend lines estimates, (b) a very good progress monitoring data set is used, and (c) the data set comprises a minimum of 14 CBMs-R. The article discusses implications and future directions. (Contains 5 tables and 2 figures.)