This study investigated the Omani English teachers' and trainers' perceptions of the effectiveness of three training courses conducted in South Batinah governorate. These courses are Cycle One (C1), Cycle Two (C2) and Post-Basic (PB) courses. 60 English teachers who attended the last version of each course as well as the two trainers of the courses participated in the study.The study aimed at answering the following five research questions: 1. What are the teachers' perceptions of the effectiveness of Cycle One, Cycle Two and Post-Basic courses? 2. What are the trainers' perceptions of the effectiveness of Cycle One, Cycle Two and Post-Basic courses? 3. What effects did the continuous professional development courses have on teachers' professional development? 4. To what extent did the teachers implement what they have learned in the courses in their classrooms? 5. What were the challenges, if any, that the teachers faced while implementing what they had learned in the courses in their teaching contexts as perceived by the teachers?The study adopted the mixed-method approach by collecting quantitative data from teachers using a questionnaire and also collecting qualitative data from the trainers via semi-structured interviews. The study is important to measure the effectiveness of specific Continuous Professional Development (CPD) courses and the effects these courses have on teachers.The findings revealed that 81.8% perceived C1 course as effective, but this percentage dropped in C2 and PB courses with 56.5% and 60% respectively who perceived the courses as effective. This means that a considerable percentage of the participants, specifically C2 and PB, perceived the courses as moderate and low effective. In addition, the participants had different views on their classroom practices and implementation of new knowledge and skills after participating in the courses. Moreover, the study found that crowded classes, workload and time constraints as the major challenges that teachers had in their classes which hindered them from implementing the new knowledge and skills.The qualitative data revealed that trainers perceived the courses as effective, which goes in harmony with what the teachers perceived. However, the qualitative data also revealed that the top-down training system had a negative impact on the courses which resulted in some shortcomings regarding the effectiveness of these courses. These shortcomings included the lack of training needs analysis prior to nominating teachers to the courses, lack of follow-up to teachers after the completion of the courses, and some contradictions that trainers had regarding assessment and challenges that teachers faced in their classrooms after the completion of the courses. These shortcomings seemed to be caused by the rigid top-down transmissive training. Therefore, some recommendations and implications were given at the end of the study to improve the effectiveness of the courses.