Few studies in language teacher education programs provide insight on how knowledge of Systemic Functional Linguistics (SFL) is developed by teacher candidates to support their metalinguistic awareness and preparation to teach language. Building upon the contributions of Johnson and Byrnes, we combined Halliday's language-based theory of learning with a sociocultural view of the development of an SFL knowledge base for language teaching. Specifically, we examined teacher candidates' development of SFL as analytical tool of their English language usage to inform and improve their eventual teaching of a language. We analyzed the functional language features that seven language teacher candidates referenced and applied in multiple drafts of SFL-driven text analyses. Our analysis focused on the ways they expressed information, negotiated relationships, and organized their messages. Results revealed four phases characterizing teacher candidates' development of more "scientific" notions of SFL whereby they (a) interpreted the meaning of text, (b) linked the meaning of text with SFL features, (c) connected SFL features to their functions, and (d) combined SFL features to enhance analysis. Implications are suggested for how language teacher educators might structure the SFL learning experiences of their language teacher candidates.