This study investigated the relationships between prospective teachers' STEM activity preparation skills (STEMaps), genders, and mathematics achievements (MA). In the research, a total of 89 prospective elementary school teachers participated. Data were collected by STEM Activity Preparation Forms requiring prospective teachers to prepare STEM activities about science experiments at the elementary school level. Relational screening model was used in the research and the relationships between STEMaps, gender and MA were tested using structural equation modeling. The findings indicated that MA has significant effects on STEMaps whereas gender has no significant effects. The path from MA to STEMaps was found to be a medium effect. It was also concluded that MA explains 20.25% of total variance of STEMaps. More longitudinal and experimental studies are needed to better understand the teachers' and prospective teachers' skills to prepare STEM activities.