Research has shown that when students are learning to reflect, their reflection is mainly descriptive. The literature describes a variety of ways to help students start reflective thinking and writing, however there are fewer suggestions for supporting them to progress from descriptive to analytical levels of reflection. This small-scale action research study examines the use of a structured selfassessment tool to deepen reflection. Data are drawn from a group of student teachers who kept reflective journals during an initial teacher training programme over one academic year. They used the tool, which provided a framework of questions about their reflective process, to assess and develop their reflective writing. In this article we discuss the effectiveness of the approach and how it promoted deeper reflection. The results indicate that the change seemed to happen through four mechanisms: revisiting reflections, using structure, taking responsibility and metacognition.