Systemic functional linguistic (SFL) theory has never acknowledged a clearcut distinction between theoretical and applied interests. Instead, the theory has tended to develop often in response to applied needs and questions, while in turn the theoretical gains that are made have tended to provoke further questions from applied contexts. The emergence of language in education theory, one of the primary applied interests in SFL theory, reveals how successful has been the dialogue between theoretical questions and applied questions. Two important themes in SFL theory, having significance for the emergence of language in education theory in Australia since the 1960s, have involved models of register and register variation on the one hand, and models of the functional grammar on the other hand. Register theory and the related theory of genre associated with the ‘Sydney School’ of SFL linguists, have developed considerably, helping to provide models of language for teaching and learning. The descriptions of the grammar, in terms of the metafunctions and in terms of systematic accounts of differences between speech and writing, have significantly enhanced theories of pedagogy and of language in education more generally. Much more work remains to be done in developing accounts of the grammar for teaching to the different age groups across the years of schooling. Systemic functional linguistic (SFL) theory has never acknowledged a clearcut distinction between theoretical and applied interests. Instead, the theory has tended to develop often in response to applied needs and questions, while in turn the theoretical gains that are made have tended to provoke further questions from applied contexts. The emergence of language in education theory, one of the primary applied interests in SFL theory, reveals how successful has been the dialogue between theoretical questions and applied questions. Two important themes in SFL theory, having significance for the emergence of language in education theory in Australia since the 1960s, have involved models of register and register variation on the one hand, and models of the functional grammar on the other hand. Register theory and the related theory of genre associated with the ‘Sydney School’ of SFL linguists, have developed considerably, helping to provide models of language for teaching and learning. The descriptions of the grammar, in terms of the metafunctions and in terms of systematic accounts of differences between speech and writing, have significantly enhanced theories of pedagogy and of language in education more generally. Much more work remains to be done in developing accounts of the grammar for teaching to the different age groups across the years of schooling.