Data-based decision-making, which involves evaluating students' progress and making instructional decisions, is an integral competency for preservice teachers. Several studies have found that visual aids, such as decision-making models, may be an effective way to train preservice teachers to make instructional decisions. The purpose of this study was to investigate the effects of a decision-making model, with and without supplemental online instruction, on U.S. preservice teachers' accuracy in identifying data patterns and making data-based decisions. Results showed that participants in both the decision-making model only and online training plus decision-making model groups had greater accuracy compared with participants who received no training. However, there were no significant differences between the two treatment groups, suggesting that the decision-making model may stand alone as an effective intervention to train preservice teachers to identify a data-based decision. Implications for research and practice are discussed.