Children and youth with autism spectrum disorders (ASD) or emotional and behavioral disabilities (E/BD) often exhibit challenging behavior including aggression, self-injury, non-compliance, or property destruction (Kamps, Kravits, Rauch, Kamps, & Chung, 2000; National Autism Center, 2009). As a result, students with ASD or E/BD often miss out on critical opportunities for learning due to their challenging behavior.Fortunately, the literature provides information on the effectiveness of functional behavioral assessment (FBA) to assess or reduce challenging behavior and increase appropriate behavior of children and youth with ASD or E/BD (e.g., Hanley, Iwata, & McCord, 2003; Horner, Carr, Strain, Todd, & Reed, 2002; Lane, Kalberg, & Shepcaro, 2009; Simpson, 2005). Functional analysis (FA), conducted as a component of FBA or alone, is specifically used to identify the function of targeted challenging behavior via a systematic experiment. The literature suggests the importance of FA as a more valid method than indirect methods or descriptive analyses in identifying behavioral functions (Asmus, Vollmer, & Borrero, 2002). FA is the only method that can demonstrate a causal relationship between an antecedent stimulus or reinforcer and a behavior (Asmus et al., 2002); however, FA is rarely used in school settings. A possible reason is associated with the complexity of FA procedures (e.g., manipulating stimuli accurately) and time constraints. To address these issues, many variations to the standard FA have been made, including trial-based FA (i.e., TBFA).In addition to the need for accurately identifying the function of students' challenging behavior, there is also a critical need for the design and implementation of function-based interventions (FBI) for students in school settings (Scott & Kamps, 2007). Interventions based on behavioral functions are essential in educational settings, especially for students with ASD or E/BD due to their susceptibility to receive disciplinary actions because of their challenging behavior. In order for FBI to be effective in addressing challenging behavior, research on FA and professional development for special education teachers is crucial.The current study used a multielement research design (Kazdin, 1982) to determine the function of six student participants' challenging behavior using TBFA in the classroom setting. Data on teacher participants' acquisition of skills learned after TBFA and FBI training and performance feedback, and their effect on students' challenging and replacement behaviors were evaluated using a multiple-probe-across-participants research design (Horner & Baer, 1978) in the classroom setting. Findings indicated that all three teacher participants were able to implement TBFA during TBFA with feedback conditions and FBI during FBI with feedback conditions with high procedural integrity. In addition, two of three teachers maintained high procedural integrity during generalization measures. Findings also indicated a reduction in students' challenging behavior and an increase in replacement behavior after training. Finally, social validity data suggested teachers felt that TBFA and FBI had an overall positive impact on student behavior. Limitations of the study, suggestions for future research, and implications for practice are also discussed.