Considering the essential role that socio-motivational relationships at school play with respect to achievement motivation, this study examined the differences between students with a low school self-concept and students with a high school self-concept in a large sample of 7th and 8th grade students (N= 1088; M[subscript Age]= 13.7) in secondary schools in Brandenburg, Germany. Multi-group structural equation modelling was used to estimate the associations between the variables of socio-motivational support and achievement motivation. The results showed that students with a high school self-concept report higher levels of socio-motivational support than students with a low school self-concept, whereas a teacher plays a more important role in motivating low self-concept students. Furthermore, the results underline the importance of adjusting the teacher's support to the level of the student's school self-concept as one of the possible prevention and intervention strategies aimed at boosting adolescents' achievement motivation after the transition to secondary school.