In Sweden, a new curriculum and new methods of assessment (grading of students and national tests) in science education were introduced in grade 6 in 2012/2013. We have investigated what implications these reforms have for teachers' teaching and assessment practices in order to explore the question of how teachers transform their teaching habits in relation to policy reforms. Interviews with 16 teachers teaching science in grade 6 (Y6), over 3 years after the reforms were introduced, were analysed. Building on the ideas of John Dewey, we consider teachers' talk about their everyday practice as expressions of their habits of teaching. Habits of teaching are related both to individual experiences as well as institutional traditions in and about teaching. A categorisation of educational philosophies was used to teachers' habits of teaching to a collective level and to show how habits can be transformed and developed over time in specific sociocultural contexts. The teachers were categorised as using essentialist and/or progressivist educational philosophy. In the responses to the introduction of grading and national testing, the teachers took three approaches: Their habits being reinforced, revised or unchanged in relation to the reforms. Although the responses were different, a striking similarity was that all teachers justified their responses with wanting to do what is best for students. However, how to show care for students differed, from delivering scientific knowledge in alignment with an essentialist educational philosophy, to preparing students to do well on tests, to supporting their development as individuals, which is in alignment with a progressivist educational philosophy.