["Psychology in the Schools, EarlyView. ", "\nABSTRACT\nDespite the growing interest in basic psychological needs within educational settings, existing measures fail to distinguish between students' relationships with teachers and classmates, limiting the understanding of how different social dynamics uniquely impact need satisfaction and frustration during adolescence. This study provided psychometric evidence for a refined school‐specific version of the Basic Psychological Need Satisfaction and Frustration Scale (BPNSFS), while also assessing differences in the satisfaction and frustration of psychological needs between early adolescents and adolescents, in Italy and the United Kingdom. A total of 1523 students (49.6% female; mean age = 12.84) completed the refined BPNSFS, specifically designed to separately measure dimensions of relatedness with classmates and teachers. Measurement invariance of the scale was established across age, sex, socio‐economic status, and country, and its scores were found to predict students' emotional experiences at school. A Multiple Indicators Multiple Causes (MIMIC) model revealed that adolescents reported greater autonomy satisfaction and frustration, higher competence frustration, lower satisfaction with classmates, and higher frustration with teachers compared to early adolescents. These findings highlight the importance of assessing relatedness needs separately for teachers and classmates, and they suggest the need for age‐specific strategies to support students' well‐being."]