This article addresses questions relative to teachers of mathematics and sciences. We first establish the notion of the specificity of both disciplines as an epistemological background to underpin our ways of tackling questions about teachers’ practices, knowledge and training initiatives. Addressing issues about practices (of teachers and of teacher education) in relation to each disciplines’ specificity invites taking into account the nature of scientific and mathematical activity in itself. These orientations lead to consider the possibilities, in contrast to prescriptions, for adressing issues of teachers’ knowledge and practices, and their implications for teacher education practices.