This study presents the account and analysis of an attempt to make the development of higher-level reflection skills an explicit learning outcome on a Trinity College London CertTESOL course. It analyses the effect that this attempt had on the depth of the written reflections of trainee teachers, and attempts to uncover their perceptions of their own development. Previous work has examined the effect of interventions to encourage the development of reflective skills in preservice state-school teacher education and in-service teacher training. However, it has not addressed such an intervention on a TESOL Certificate course. The present study draws on the relevant literature to design a process of reflection, and analyses its effectiveness. Qualitative analysis consists of deductive analysis of participants’ written reflections and inductive analysis of transcripts from semi-structured interviews. Findings show that trainees developed their reflective skills, could use their reflections to adapt their teaching, and were aware of their own development. It concludes that aspects of TESOL Certificate courses are conducive to the development of reflective skills, and suggests a procedure which can maximise the benefits of these aspects and a level of reflection appropriate as a learning aim of such a course.