This paper describes the confirmatory factor analysis, validity, and reliability data collection stage of the development of a scale to measure mainstream teachers' self-efficacy beliefs for teaching ELL (English Language Learner) students. Data were collected from 708 K through 12 teachers and pre-service teachers with varying degrees of training specific to teaching ELL students. Using confirmatory factor analysis, a 23 item scale consisting of two factors "instruction and assessment" (14 items) and "native language support and resources" (9 items) was assessed for model fit. The data were not a good fit for the hypothesized two factor model (CFI = 0.82, RMSEA= 0.12). Additionally, the scale was positively correlated with social desirability. However, the scale maintained adequate convergent and discriminant validity with measures of culturally responsive teaching self-efficacy, multicultural teaching competencies, satisfaction with life, and self-esteem. The scale also demonstrated strong internal consistency and test-retest reliability. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]