As online education grows rapidly in social work, there are growing concerns about teaching critical-thinking skills in online environments. This retrospective case study shares experience of an online course that employed a strength-based instructional method to enhance critical-thinking skills among undergraduate social-work students. Twenty-two student assignments were reviewed from an online Human Behaviour and Social Environment course offered to undergraduate social-work students. Three approaches were adopted to learn the impact of instructional practices on critical-thinking skills: 1) students’ course evaluations; 2) the number of words written in students’ responses to written assignments; 3) the quality of students’ prompts. The study found that using a strength-based approach and providing individualised feedback were effective in enhancing critical-thinking skills in online courses. Limitations and suggestions for future research were discussed.