Thai students study English as a compulsory subject for twelve years in primary and secondary school, yet their English language competency is generally lower than other ASEAN countries. This might have been attributed to the teacher-centred approach in EFL classrooms. Active learning has been suggested as a better approach for English learning in Thai school, but more research is needed to confirm the previous findings in the Thai context. This study investigated the practices and perceptions of 41 school teachers after 40 hours of training on the active learning approach. Observation, questionnaires, and interviews were administered. The findings revealed the positive effects of active learning on teachers' perceptions, and classroom observations showed that the approach implemented in the classroom were moderately practical. However, the findings from classroom observation disclosed that classroom facilities did not fully support active learning. The findings of interviews unveiled some negative impacts of active learning that could hinder the effective implementation of active learning in the classroom such as limited resources, space, and time, as well as challenges in classroom management. Overall, teachers' perceptions of the active learning approach was positive.