Teacher professional development (TPD) frequently fails to produce sustained classroom implementation due to top-down designs that neglect teacher realities. This case study explored Thai secondary English language teachers’ preferences for TPD initiatives in Khon Kaen Province, Thailand, addressing the execution gap between training acquisition and real-world instruction. Guided by a case study design, data collection was conducted in two sequential stages. First, an online survey gathered preliminary data from 221 public secondary school English teachers. Subsequently, qualitative semi-structured interviews were conducted with 16 teachers possessing 5 to 10 years of experience and participation in over five Ministry-sponsored TPD programs. Survey data were evaluated using descriptive statistics, while interview transcripts were analyzed using thematic analysis. Analysis of 274 relevant teacher statements identified three core themes defining effective TPD: TPD with knowledge application (64.96%), TPD with collaboration (20.80%), and TPD with feedback/follow-up process (14.23%). Within knowledge application, teachers prioritized hands-on activities (42.70%), such as micro-teaching, and contextually relevant content (22.26%). Qualitative findings confirmed that teachers value practical, interactive experiences matched to their classroom contexts and view structured follow-up as vital for evaluating sustained instructional impact. Effective TPD requires shifting from top-down, lecture-style models toward teacher-centered, agency-driven frameworks. Incorporating pre-training needs assessments, hands-on activities, context-matched content, and systematic feedback mechanisms enhances teacher engagement and pedagogical transfer. Educational leaders and policymakers must prioritize teacher input to design sustainable professional learning that directly improves language classroom instruction.