Previous research suggests that normative life transitions have the potential to trigger personality maturation. But what exactly happens during such a transitional stage? The present study examined personality trait changes in a sample of 910 German high school students during their transition from school to adult life. Despite the short observation period of three semiannual measurements, growth curve analyses revealed significant mean-level changes in personality traits. These changes occurred primarily in a positive direction, were strongest for the trait of conscientiousness, and most pronounced in those students who were directly confronted with this transitional experience. Bivariate growth curve models indicated that individual differences in personality change were substantially associated with changes in students’ investments into achievement behavior. Supporting socioanalytic perspectives on personality development, these findings can be discussed with respect to process approaches to personality change assuming that consistent behavioral changes might lead to personality change in a bottom-up fashion.