In STEMNET's report, 76% of 500 teachers interviewed stated that joining the STEM Club increased students' ability to solve real-world problems. This study aims to develop a valid and reliable measurement tool for evaluating STEM clubs. The research sample consisting of 149 teachers who carry out STEM club activities in schools in Turkey was determined using the purposive sampling method. Content and construct validity and reliability analyses have been performed for this purpose. To ensure content validity, (1) a pool of questions based on the literature was created, (2) draft scale items were determined, (3) an expert was allowed to check them, and (4)item difficulty and discrimination index were calculated. To ensure construct validity, (1) exploratory factor analyses (EFA) and (2) confirmatory factor analyses (CFA) were performed on both the same and different samples. As a result of the analyses, having the same data set be analyzed with different software was sufficient for verifying the factor structure. A three-factor structure consisting of 29 items was obtained, which explains 52% of the variance. Cronbach’s alpha of reliability for the overall scale was calculated as .92. As a result, a valid and reliable scale was determined to have been developed for researchers and program practitioners to evaluate STEM clubs. Suggestions have been made that the scale can be used on STEM clubs at the provincial, district, and school levels to determine their efficiency and productivity.