The research objectives were to 1) study Thai PD project features, 2) synthesize Thai regional factors affecting teacher performance, and 3) present the guideline of PD activities for STEM education at the primary level. The sample group was the two years research project reported in 2021 on PD for primary science teachers' training programs in STEM education in Thailand. The meta-analysis was used to synthesize the results from training groups. The research instruments were a checklist of the PD project features form and guidelines for the PD evaluation form. The qualitative data were analyzed using content analysis. The statistics used for data analysis were mean standard deviation and one-way ANOVA. As the results, they indicated that: 1) Thai PD project had high-quality components based on experts in the field. Mainly features showed the process of checking the quality of curriculum program and received a good amount of feedback, 2) the analysis results showed no evidence of regional difference affecting teachers' performance at 0.05 confident level, and 3) there were 6 modules for training activities empowering primary science teachers in STEM. There were recommendations for using this PD in STEM education at different levels of education, but needs adjusted activities and time duration of each step in PD, and STEM learning should be integrated into other studies such as in art and history.