Purpose: This study analyzed whether the psychosocial school environment mitigates the detrimental effects of poverty and influences students' initial cognitive (Korean, math, and English grades) and emotional (self-esteem) development during elementary school, as well as their growth trajectories throughout middle and high school. Methods: This study used longitudinal data from the same cohort of students surveyed at three intervals: elementary, middle, and high school spanning a six-year period from 2015, to 2018 and 2021. Data were obtained from the Korea Welfare Panel Study Supplementary Survey on Children.Analysis was conducted using the Multilevel Growth Model to examine the cognitive and emotional development trajectories of students throughout their elementary, middle, and high school years. Results: In terms of cognitive development, the study found that teacher support within the psychosocial school environment positively influenced the growth rate of Korean language subject grades. Regarding emotional growth, factors such as teacher support, school atmosphere, and peer relationships within the psychosocial school environment all exhibited significant positive effects on the initial levels of self-esteem among elementary school students. Additionally, the school atmosphere positively impacted the growth rate of self-esteem. The negative impact of poverty was often diminished or mitigated with the inclusion of variables such as students’ learning attitudes and parental educational involvement and supervision. Furthermore, with the additional inclusion of psychosocial school environment variables, the adverse effects of poverty almost completely disappeared. However, the influence of poverty persisted, manifesting as a negative impact on the initial scores of English subject grades. Conclusion: The psychosocial school environment can positively contribute to students' cognitive and emotional development. Particularly, teacher support has a positive impact on both the cognitive and emotional growth of students, and school climate and peer relationships are positively associated with emotional development. Therefore, efforts should be made in schools to strengthen teacher support, and to foster a positive school climate and peer relationships, aiming for a positive direction in cognitive and emotional development.