Secondary school students find it difficult to write elaborated causal explanations of scientific phenomena. They frequently present their own opinions and write descriptions of their observations rather than linking observations with logical chains of causal reasoning, underpinned by a theoretical framework, to provide explanations of scientific phenomena. Science teachers also express difficulties in supporting students to develop scientific writing skills. In order to improve students’ written scientific explanations, a teaching strategy known as the Thinking Frames Approach (TFA) was introduced into two Grade 9 classrooms over two years. This multidimensional conceptual change strategy makes use of the affordances of student-generated multiple representations, teacher-student questioning, and small group discussions to support students in constructing understanding and written explanations. Students are also taught to reflect on and evaluate their written explanations. Students’ written responses explaining observations of scientific phenomena were collected over a nine-month period and evaluated using the analysis system for student explanations developed by de Andrade et al. (Res Sci Educ 49:787-807, 2019). A significant improvement in students’ written explanations linking observations with logical chains of reasoning and scientific theories was observed over this period. The TFA provides a strategy that teachers may implement to support students in developing skills in writing explanations by providing an appropriate level of scaffolding in the writing process. An added benefit of this approach was students’ increased confidence in producing written explanations.