Research on perceived instrumentality of students' academic work for attaining life goals has shown to have positive effects on academic achievement and motivation The purpose of the study was to examine the changes in perceived instrumentality over time and to identify how significant others such as parents, teachers and peers affect changes in perceived instrumentality. The variables of gender, prior achievement levels, academic pressure and socioeconomic status, which had significant influences on perceived instrumentality according to previous research, were used as control variables. Longitudinal data were collected for four years of 6908 students and analysed using the Growth Curve Modelling technique. Parents' and teachers' academic expectations and their career guidance, and social support from peers were used as predictors for changes in perceived instrumentality. Our results revealed that perceived instrumentality increased over time but in a decelerated pattern. In addition, parents and peers had significant influences on perceived instrumentality and its change, but teachers did not. The results suggest that support from parents and peers helps students to understand and internalise why they have to study hard in school to achieve their future long-term life goals.