In Malaysia, literature relating to the efficacy of STEM learning has been limited to secondary or tertiary levels, and remains more popular among the school populations. However, in terms of the influence of social support on the development of learners' STEM efficacy (SE), the fathers' impact has been neglected. To bridge this gap, this study explored the influence of fathers' support on SE. Based on theoretical insights, hope was included as a mediator to hypothesise a potential underlying process that determines the relationship between fathers' support and SE. This was a quantitative study that employed a correlational research design. It involved 548 young adolescents aged 9 to 11 years, who studied in government primary schools, and lived in the Klang Valley. Regression analysis using Structural Equation Modelling (SEM) showed that fathers' involvement (b=.284, p=.002), and structure support (b=.275, p=.000) uniquely predicted SE, but had no effect on autonomy support. Hope significantly mediated the relationships between involvement and SE, and between autonomy support and SE, but showed no mediating effect on structure support. This study offers several implications. First, it unfolded hope as a significant underlying factor mediating the relationships between fathers' support and SE. Second, it expanded the literature on fathers' support and SE with the population of young learners. Lastly, by revealing the predictors of SE as well as the mediating role of hope, this study provides implications for future STEM educational planning at the primary school level in Malaysia.