Though it is well-established that self-esteem develops from childhood well into old age, little is known about the processes that influence this change, especially among young populations. This international, cross-sequential study examined the development of self-esteem in 1599 second-graders (Age M T1 = 7.99, SD T1 = 0.52 years; 52% male) in the Netherlands and Germany over three years. Multilevel models revealed that mean-level trends in self-esteem were stable across time among all demographic groups, but that males and students in the Netherlands consistently had higher self-esteem than females and students in Germany. Further analyses examining the role of social support in self-esteem development demonstrated that individuals with better peer and family social support tended to have higher levels of self-esteem and that within-person changes in social support were directly related to changes in self-esteem level, providing support for sociometer theory. These findings suggest that demographic factors as well as social support are important predictors of self-esteem as early as middle childhood.