The present study investigates the use of critical reflection as formative assessment of learning outcomes in the context of English as a foreign language. It aims to explore learners’ perception of how effective critical reflection is on the learning quality of knowledge and skills outcomes. Data was obtained from a purposeful sample of 113 participants who used critical reflection to assess their own learning quality against lesson learning outcomes. A questionnaire was employed to elicit responses on the learners’ experience of using critical reflection as well as self-assessment on their own learning quality. The results from pair samples t-test revealed that the participants’ use of critical reflection resulted in differing extents of achievement of knowledge outcomes and skills outcomes. While the findings suggest the helpfulness of the critical reflection as a means of self-assessment, they raised a question of designing critical reflection in a way it is better suited to different types of learning outcomes for optimal implementation in English classrooms.