Abstract: This study evaluated whether or not teachers of students with severe disabilities reported implementing specific data-based decision guidelines to make instructional decisions (Browder, Liberty, Heller, & D'Huyvetters, 1986; Browder, Demchak, Heller, & King, 1989) following completion of their teacher preparation program. A cross-sectional survey regarding reported accuracy was followed by examination of teacher-submitted student performance data sheets to determine actual accuracy. A majority of respondents reported currently using the decision guidelines or using the guidelines in the past. Survey results indicated teacher perception of accurate use was high, while data sheet evaluation indicated actual accuracy was questionable and generally low. Teachers reported having lower confidence and accuracy in their actions related to data analysis than data collection. The actual data sheets supported their reports; steps and actions of the decision guidelines with the lowest accuracy of use were related to data analysis and instructional decisions. We discuss implications and suggestions for increasing accurate use of the data-based decision-making guidelines.