Oral language is foundational to literacy. Because their language is under construction, emergent bilingual students have unique needs related to literacy development regardless of the language of instruction. Knowledge teachers gain through formative assessment of student oral language can guide decisions about literacy instruction. The purpose of this mixed-methods study was to explore the knowledge and practice of formative oral language assessment among literacy intervention teachers working in California public bilingual school settings with Spanish-English emergent bilingual students in kindergarten through second grade, and to investigate the extent to which formative language assessment tools were available and used by literacy intervention teachers. This study was guided by the following two research questions: (1) Teacher knowledge: What do literacy intervention teachers know about bilingual oral language development; its role in literacy development of their emergent bilingual students; and formative language assessment? and (2) Teacher practice: What do literacy intervention teachers do to formatively assess the oral language of Spanish-English emergent bilingual students? Results suggest teachers conflate oracy and literacy in assessment and teachers lack appropriate formative language assessment instruments. Findings suggest practice might be improved by enhancing teacher knowledge through training and professional development, providing opportunities for professional collaboration, and increasing advocacy for effective literacy and language interventions. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]