How can researchers better understand the mindsets of educators regarding their work with parents in order to build better relationships among adults to support each and every child? Before recently, a lack of clarity about the domain of educators' work when engaging with parents and caregivers stymied efforts to investigate educators' mindsets about family engagement. This study explored the nature of teachers' family engagement efficacy beliefs and developed a measurement instrument, the Family Engagement Efficacy Beliefs of Educators (FEEB-E) survey. An interpretation-use argument approach (Kane, 2016) guided the validation of its scores. Analysis of data from an administration of FEEB-E to 318 family-facing professionals indicated the FEEB-E items to be representative of family engagement efficacy beliefs, an adequate and reliable representation of the beliefs of the sample, without extraneous sources of variability, and, taken together, appropriate for use as a research instrument.