The current study used a randomized control trial to evaluate a decision-making model on special education preservice candidates' instructional decision-making and self-reported confidence ratings when analyzing graphed student data. Thirty-two special education preservice candidates viewed authentic curriculum-based measurement (CBM) graphs and selected an instructional decision based on the data. Half of the participants received a decision-making model (i.e., flowchart) to guide instructional decision-making and all participants were asked to rate their level of confidence analyzing graphs pre- and poststudy. Statistically significant and large differences in the accuracy of instructional decisions and confidence ratings were observed for the participants who used the decision-making model relative to the control group. The results of the study suggest that a simple, cost-effective intervention that does not require training from an expert can have a positive impact on teachers' data-based decision-making.