https://doi.org/10.1177/0731948719840774 Learning Disability Quarterly 1–14 © Hammill Institute on Disabilities 2019 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0731948719840774 journals.sagepub.com/home/ldq Original Research Ensuring fidelity of implementation is critical to an inter- vention’s success (O’Donnell, 2008). Fidelity of implemen- tation can be measured during one or more stages of intervention development, including (a) development and pilot testing, (b) efficacy trials, (c) research at scale, and (d) application in real-world settings (Smolkowski & Crawford, this issue). This article explores implementation fidelity as related to Stage 1, the design and initial testing of an inter- vention (Onken, Blaine, & Battjes, 1997). Questions about implementation fidelity at Stage 1 concern themselves with the what, why, and how of an intervention (Hulleman & Cordray, 2009). As an example, Doabler et al. (2015) illus- trate this relationship between theory (why), curriculum (what), and practice (how), in their paper on the design and development of a Tier II mathematics intervention. In con- trast, implementation fidelity questions asked during other stages of the research process investigate “how much” (e.g., dosage) and “how well” (e.g., integrity; see, for example, Harn, Parisi, & Stoolmiller, 2013; Woodbridge et al., 2014). Answers to all of these questions are important to assuring an intervention’s fidelity of implementation as a necessary component in an evidence-based intervention (Fixsen, Naoom, Blase, Friedman, & Wallace, 2005). Stage 1 activities undertaken during the design and devel- opment of a Tier II fraction-based mathematics intervention (the fractions intervention) are the topic of this article. The intervention focused on developing the fraction number sense (Siegler, Fazio, Bailey, & Zhou, 2013), or fraction- sense, of students with learning disabilities (LD) or difficul- ties in fifth and sixth grade. Specifically, the intervention prompted students to explore and explain number patterns to better understand fraction magnitude and demonstrate this understanding by comparing and ordering fractions of dif- ferent sizes through use of traditional paper and pencil tools or various technology-based supports such as audio record- ing, keyboarding, and drawing tools (all of which were intended to support students’ conceptual understanding). Four steps undertaken during the design and develop- ment of the fractions intervention are detailed in this article: (a) articulation of a logic model influenced by theoretical frames of reference, (b) delineation of the components included in the intervention hypothesized to improve 840774LDQ XX X 10.1177/0731948719840774Learning Disability QuarterlyCrawford et al. research-article 2019 1 Texas Christian University, Fort Worth, USA 2 University of California, Berkeley, USA 3 University of Nebraska–Lincoln, USA 4 Tarleton State University, Fort Worth, Texas, USA Corresponding Author: Lindy Crawford, ANSERS Institute, Texas Christian University, TCU Box 297900, Fort Worth, TX 76129, USA. Email: lindy.crawford@tcu.edu Implementation Fidelity and the Design of a Fractions Intervention Lindy Crawford, PhD 1 , Barbara Freeman, EdD 2 , Jacqueline Huscroft-D’Angelo, PhD 3 , Sarah Quebec Fuentes, EdD 1 , and Kristina N. Higgins, PhD 4 Abstract Interventions are implemented with greater fidelity when their core intent is made explicit. The core intent of this intervention was to increase access to higher order learning opportunities for students with learning disabilities or difficulties in mathematics through use of research and practice from the fields of special education and mathematics education. Four steps undertaken in the development of a Tier II fraction-based mathematics intervention designed to improve the conceptual understanding of students with learning disabilities or difficulties are described in this article: (a) articulation of a logic model, (b) delineation of intervention components, (c) analysis of reliability data related to implementation fidelity, and (d) pilot testing to measure implementation fidelity and student outcomes. Results of the pilot study demonstrated no significant effect for the component of technology; however, significant pre–post differences were found in the performance of all groups on their conceptual understanding of fractions as numbers. Keywords implementation fidelity, fractions, intervention, learning disabilities, technology