Although function-based treatments have been proven to decrease challenging behavior, it is unclear whether these results translate to socially significant outcomes. In fact, researchers rarely analyze what happens outside the highly controlled setting in which behavior analytic sessions typically occur. In our first study, we used a changing criterion design to evaluate the effectiveness of using the Function-Informed Mechanisms-Based (FIMB) framework to increase levels of replacement behaviors and decrease tantrum behavior for three children with IDD (i.e., a single sibling set) and a history of severe challenging behavior. In the second study, we discussed caregiver reports of the children's behavior outside of treatment, offering a more nuanced understanding of data patterns included in Study 1. By embedding a structured process of formative data triangulation, researchers expanded the existing treatment plan to promote generalizable decreases in challenging behavior and socially significant improvements in the family's quality of life. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]