With the recent increase in the use of functional behavior assessment (FBA) in school settings, there has been an emphasis in practice on the development and use of effective, efficient methods of conducting FBAs, particularly indirect assessment tools such as interviews. There are both benefits and drawbacks to these tools, and their technical adequacy is often unknown. This article presents a framework for assessing the measurement properties of FBA interview tools and uses this framework to assess evidence for reliability and validity of one interview tool, the Functional Assessment Checklist: Teachers and Staff (FACTS; March et al., 2000). Results derived from 10 research studies using the FACTS indicate strong evidence of test—retest reliability and interobserver agreement, moderate to strong evidence of convergent validity with direct observation and functional analysis procedures, strong evidence of treatment utility, and strong evidence of social validity. Results are discussed in terms of future validation research for FBA methods and tools.