Many teachers struggle to deliver interventions with sufficient treatment integrity, perhaps due to implementation variables that mediate or moderate treatment integrity. Potential implementation variables have frequently been conceptualized in ecological frameworks, including the intervention, implementer, organization, and external environmental levels. Although the ecological framework is a useful organizational tool, a measure aligned with this model of implementation variables has not yet been developed. This article describes the development of the Assessment of Ecological Implementation Influences (AEII), a measure to evaluate implementation variables across ecological levels. Exploratory factor analyses were conducted to evaluate to what extent responses on the AEII reflect the hypothesized ecological factor structure. The model of variables from the intervention to external environment level was not reflected within the factor structure here. Rather, factors emerged that were not previously accounted for in the implementation variables literature. Implications for future research on the measurement of treatment integrity and implementation variables are described.