This quasi-experimental study investigates the effects of the Think–Pair–Share (TPS) cooperative learning strategy on the English-speaking skills of 46 10th-grade students at a rural high school in An Giang province, Vietnam. The 12-week intervention was integrated into the English 10 textbook with weekly speaking lessons structured around three phases such as individual thinking, paired discussion, and whole-class sharing. Quantitative data were collected from pre- and post-speaking tests assessed across five domains including content, organization, pronunciation, grammar, and vocabulary. Complementary qualitative data were obtained through semi-structured interviews with ten students. The results indicated statistically significant improvements in all assessed areas. Moreover, interview data revealed enhanced learner confidence, reduced speaking anxiety, and improved idea organization through peer collaboration. While students valued the structured interaction and peer support offered by TPS, some reported challenges related to time pressure and uneven group participation. These findings suggest that TPS is an effective, low-cost instructional strategy for fostering communicative competence in English as a foreign language, particularly in under-resourced rural contexts. The study highlights the pedagogical potential of TPS for promoting interactive speaking practice in secondary EFL classrooms and calls for further research into its long-term effects and adaptability across different learner populations.