We conducted 2 experiments in which we used an informant-based assessment tool (i.e., the Performance Diagnostic Checklist–Parent; PDC-P) to identify an intervention specifically targeted to address the variables responsible for deficient intervention plan implementation by parents. In Experiment 1, we administered the PDC-P to 3 parents who were inaccurately implementing their child’s mand training program. We then evaluated an intervention designed to address the reason for deficient program implementation identified by the assessment tool. In Experiment 2, we administered the PDC-P to 3 additional parents. We then compared an intervention not indicated by the tool to a PDC-P-indicated intervention. Across both experiments, results indicated that the PDC-P was useful to identify an effective intervention to increase accurate implementation of mand training for all parent participants. In Experiment 2, the indicated intervention was more effective than the nonindicated intervention to improve parent performance. Furthermore, performance improvements sustained for up to 8 (Experiment 2) or 12 (Experiment 1) weeks for some parents. Accurate use of mands improved for some, but not all, children. (PsycInfo Database Record (c) 2020 APA, all rights reserved)